     #include <bits/stdc++.h>

//    #include <boost/multiprecision/cpp_int.hpp>
// #define int long long
 #define inf  1000000007
 #define pa pair<int,int>
 #define ll long long
 #define pal pair<double,double>
 #define ppap pair<pa,int>
  #define PI 3.14159265358979323846
  #define paa pair<int,char>
  #define  mp make_pair
  #define  pb push_back
  #define EPS (1e-10)
                                          
    int dx[8]={0,1,0,-1,1,1,-1,-1};
    int dy[8]={1,0,-1,0,-1,1,1,-1};
                                            using namespace std;
                                   			class pa3{
                                            	public:
                                            	int x,y,z;
                                            	pa3(int x=0,int y=0,int z=0):x(x),y(y),z(z) {}
                                            	bool operator < (const pa3 &p) const{
                                            		if(x!=p.x) return x<p.x;
                                            		if(y!=p.y) return y<p.y;
                                            		 return z<p.z;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                   				bool operator > (const pa3 &p) const{
                                            		if(x!=p.x) return x>p.x;
                                            		if(y!=p.y) return y>p.y;
                                            		 return z>p.z;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa3 &p) const{
                                            		return x==p.x && y==p.y && z==p.z;
                                            	}
                                            		bool operator != (const pa3 &p) const{
                                            			return !( x==p.x && y==p.y && z==p.z);
                                            	}
                                            
                                            };
                                            
                                            class pa4{
                                            	public:
                                            	int x;
                                            	int y,z,w;
                                            	pa4(int x=0,int y=0,int z=0,int w=0):x(x),y(y),z(z),w(w) {}
                                            	bool operator < (const pa4 &p) const{
                                            		if(x!=p.x) return x<p.x;
                                            		if(y!=p.y) return y<p.y;
                                            		if(z!=p.z)return z<p.z;
                                            		return w<p.w;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator > (const pa4 &p) const{
                                            		if(x!=p.x) return x>p.x;
                                            		if(y!=p.y) return y>p.y;
                                            		if(z!=p.z)return z>p.z;
                                            		return w>p.w;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa4 &p) const{
                                            		return x==p.x && y==p.y && z==p.z &&w==p.w;
                                            	}
                                            		
                                            
                                            };
                                            class pa2{
                                            	public:
                                            	int x,y;
                                            	pa2(int x=0,int y=0):x(x),y(y) {}
                                            	pa2 operator + (pa2 p) {return pa2(x+p.x,y+p.y);}
                                            	pa2 operator - (pa2 p) {return pa2(x-p.x,y-p.y);}
                                            	bool operator < (const pa2 &p) const{
                                            		return y != p.y ? y<p.y: x<p.x;
                                            	}
                                            	bool operator > (const pa2 &p) const{
                                            		return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa2 &p) const{
                                            		return abs(x-p.x)==0 && abs(y-p.y)==0;
                                            	}
                                            	bool operator != (const pa2 &p) const{
                                            		return !(abs(x-p.x)==0 && abs(y-p.y)==0);
                                            	}
                                            		
                                            
                                            };
                                            
/*
                                            class Point{
                                            	public:
                                            	double x,y;
                                            	Point(double x=0,double y=0):x(x),y(y) {}
                                            	Point operator + (Point p) {return Point(x+p.x,y+p.y);}
                                            	Point operator - (Point p) {return Point(x-p.x,y-p.y);}
                                            	Point operator * (double a) {return Point(x*a,y*a);}
                                            	Point operator / (double a) {return Point(x/a,y/a);}
                                            	double absv() {return sqrt(norm());}
                                            	double norm() {return x*x+y*y;}
                                            	bool operator < (const Point &p) const{
                                            		return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const Point &p) const{
                                            		return fabs(x-p.x)<EPS && fabs(y-p.y)<EPS;
                                            	}
                                            };
                                            typedef Point Vector;
                                     #define pl pair<int,pas>
                                            struct Segment{
                                            Point p1,p2;
                                            };
                                             double dot(Vector a,Vector b){
                                            	return a.x*b.x+a.y*b.y;
                                            }
                                            double cross(Vector a,Vector b){
                                            	return a.x*b.y-a.y*b.x;
                                            }
                                        
                bool parareru(Point a,Point b,Point c,Point d){
                //	if(abs(cross(a-b,d-c))<EPS)cout<<"dd "<<cross(a-b,d-c)<<endl;
                	return abs(cross(a-b,d-c))<EPS;
                }
                double distance_ls_p(Point a, Point b, Point c) {
                  if ( dot(b-a, c-a) < EPS ) return (c-a).absv();
                  if ( dot(a-b, c-b) < EPS ) return (c-b).absv();
                  return abs(cross(b-a, c-a)) / (b-a).absv();
                }
                bool is_intersected_ls(Segment a,Segment b) {
                	if(a.p1==b.p1||a.p2==b.p1||a.p1==b.p2||a.p2==b.p2) return false;
                	if(parareru((a.p2),(a.p1),(a.p1),(b.p2))&&parareru((a.p2),(a.p1),(a.p1),(b.p1))){
                //		cout<<"sss"<<endl;
                		if(dot(a.p1-b.p1,a.p1-b.p2)<EPS) return true;
                		if(dot(a.p2-b.p1,a.p2-b.p2)<EPS) return true;
                		if(dot(a.p1-b.p1,a.p2-b.p1)<EPS) return true;
                		if(dot(a.p1-b.p2,a.p2-b.p2)<EPS) return true;
                		return false;
                	}
                  else return ( cross(a.p2-a.p1, b.p1-a.p1) * cross(a.p2-a.p1, b.p2-a.p1) < EPS ) && ( cross(b.p2-b.p1, a.p1-b.p1) * cross(b.p2-b.p1, a.p2-b.p1) < EPS );
                }
                 
                double segment_dis(Segment a,Segment b){
                	if(is_intersected_ls(a,b))return 0;
                	double r=distance_ls_p(a.p1, a.p2, b.p1);
                	r=min(r,distance_ls_p(a.p1, a.p2, b.p2));
                	r=min(r,distance_ls_p(b.p1, b.p2, a.p2));
                	r=min(r,distance_ls_p(b.p1, b.p2, a.p1));
                	return r;
                }
                Point intersection_ls(Segment a, Segment b) {
                  Point ba = b.p2-b.p1;
                  double d1 = abs(cross(ba, a.p1-b.p1));
                  double d2 = abs(cross(ba, a.p2-b.p1));
                  double t = d1 / (d1 + d2);
                 
                  return a.p1 + (a.p2-a.p1) * t;
                }
 */                
                                string itos( int i ) {
                                ostringstream s ;
                                s << i ;
                                return s.str() ;
                                }
                                 
                                int gcd(int v,int b){
                                	if(v>b) return gcd(b,v);
                                	if(v==b) return b;
                                	if(b%v==0) return v;
                                	return gcd(v,b%v);
                                }
                 
                                double distans(double x1,double y1,double x2,double y2){
                                	double rr=(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
                                	return sqrt(rr);
                                	
                                }
                                int mod;
int extgcd(int a, int b, int &x, int &y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }
    int d = extgcd(b, a%b, y, x);
    y -= a/b * x;
    return d;
}
    
                                
                int pr[1000010];
                int inv[1000010];
                
                int beki(int wa,int rr,int warukazu){
                	if(rr==0) return 1%warukazu;
                	if(rr==1) return wa%warukazu;
                	wa%=warukazu;
                	if(rr%2==1) return ((ll)beki(wa,rr-1,warukazu)*(ll)wa)%warukazu;
                	ll zx=beki(wa,rr/2,warukazu);
                	return (zx*zx)%warukazu;
                }
    double bekid(double w,int r){
    	if(r==0) return 1.0;
    	if(r==1) return w;
    	if(r%2) return bekid(w,r-1)*w;
    	double f=bekid(w,r/2);
    	return f*f;
    }
                
    			int comb(int nn,int rr){
    				int r=pr[nn]*inv[rr];
    				r%=mod;
    				r*=inv[nn-rr];
    				r%=mod;
    				return r;
    			}
                
                void gya(int ert){
                	pr[0]=1;
                	for(int i=1;i<ert;i++){
                		pr[i]=(pr[i-1]*i)%mod;
                	}
                	for(int i=0;i<ert;i++) inv[i]=beki(pr[i],mod-2,mod);
                	
                }
                
              //   cin.tie(0);
    		//	ios::sync_with_stdio(false);
    			//priority_queue<pa3,vector<pa3>,greater<pa3>> pq;            
                 //sort(ve.begin(),ve.end(),greater<int>());
    
                                     //----------------kokomade tenpure------------

string s[50];
int ka[50][50][50][50];
int ans[50][50][50][50];
vector<pa> ve[26];

int h,w;
int dfs(int i,int j,int x,int y){
//	cout<<i<<" "<<j<<" "<<x<<" "<<y<<endl;
	if(i>x || j>y) return -1;
	if(i<0 || i>=h) return-1;
	if(j<0 || j>=w) return -1;
	if(!ka[i][j][x][y])return -1;
	if(ans[i][j][x][y]>=0) return ans[i][j][x][y];
	if(i==x && j==y ){
		ans[i][j][x][y]=0;
		return 0;
	}
	if(s[i][j]=='.' || (s[i][j]>='A' && s[i][j]<='Z')){
		int r=-1;
		r=max(r,dfs(i+1,j,x,y));
		r=max(r,dfs(i,j+1,x,y));
		ans[i][j][x][y]=r;
		return r;
	}
	{
		assert(s[i][j]>='a' && s[i][j]<='z');
	//	cout<<s[i][j]<<endl;
		int r=-1;
		r=max(r,dfs(i+1,j,x,y));
		r=max(r,dfs(i,j+1,x,y));
		int c=s[i][j]-'a';
		for(auto v:ve[c]){
			if(i<=v.first && v.first<=x && j<=v.second && v.second<=y){
		//		cout<<"  "<<v.first<<" "<<v.second<<endl;
				if(v.first==x && v.second==y && abs(x-i)+abs(y-j)==1){
					r=1;
				}
				else if(v.first==x && v.second==y){
					int f1=-1;
					f1=max(f1,dfs(i+1,j,v.first-1,v.second));
					f1=max(f1,dfs(i+1,j,v.first,v.second-1));
					f1=max(f1,dfs(i,j+1,v.first-1,v.second));
					f1=max(f1,dfs(i,j+1,v.first,v.second-1));
					if(f1>=0) r=max(r,f1+1);
				}
				else{
					if(ka[i][j][v.first][v.second]){
						int f1,f2,f3;
						f1=dfs(i,j,v.first,v.second);
						if(f1<0) continue;
						f2=dfs(v.first+1,v.second,x,y);
						f3=dfs(v.first,v.second+1,x,y);
						f2=max(f2,f3);
						if(f2<0) continue;
						r=max(r,f1+f2);
					}
				}
			}
		}
		ans[i][j][x][y]=r;
		return r;
	}
}

int solve(){

	cin>>h>>w;
	
	if(h==0 && w==0) exit(0);
	for(int i=0;i<26;i++)ve[i].clear();
	for(int i=0;i<50;i++)s[i]="";
	for(int i=0;i<h;i++)cin>>s[i];
	for(int i=0;i<50;i++)for(int j=0;j<50;j++)for(int k=0;k<50;k++)for(int l=0;l<50;l++){
		ka[i][j][k][l]=0;
		ans[i][j][k][l]=-1;
	}
	
	for(int i=0;i<h;i++)for(int j=0;j<w;j++){
		if(s[i][j]!='#' && s[i][j]!='.'){
				if(s[i][j]<='Z')ve[s[i][j]-'A'].pb({i,j});
		}
		if(s[i][j]=='#')continue;
		ka[i][j][i][j]=1;
		for(int x=i;x<h;x++)for(int y=j;y<w;y++)if(s[x][y]!='#'){
			if(x==i && y==j) continue;
			if(x!=i){
				if(ka[i][j][x-1][y])ka[i][j][x][y]=1;
			}
			if(y!=j){
				if(ka[i][j][x][y-1])ka[i][j][x][y]=1;
			}
		}
	}
	
	if(!ka[0][0][h-1][w-1])return -1;
	dfs(0,0,h-1,w-1);
	//for(int i=0;i<w;i++)for(int j=i;j<=w;j++)cout<<i<<" "<<j<<" "<<ans[0][i][0][j]<<endl;
	return dfs(0,0,h-1,w-1);

}

 signed main(){

    	       cin.tie(0);
   			ios::sync_with_stdio(false);

 	while(1){
 		cout<<solve()<<endl;
 	}
 	return 0;
  }



### Prompt

Please provide a CPP coded solution to the problem described below:

Problem Statement

There is a maze which can be described as a W \times H grid. The upper-left cell is denoted as (1, 1), and the lower-right cell is (W, H). You are now at the cell (1, 1) and have to go to the cell (W, H). However, you can only move to the right adjacent cell or to the lower adjacent cell. The following figure is an example of a maze.


...#......
a###.#####
.bc...A...
.#C#d#.#
.#B#.#.###
.#...#e.D.
.#A..###.#
..e.c#..E.
d###.#
....#.#.#
E...d.C.


In the maze, some cells are free (denoted by `.`) and some cells are occupied by rocks (denoted by `#`), where you cannot enter. Also there are jewels (denoted by lowercase alphabets) in some of the free cells and holes to place jewels (denoted by uppercase alphabets). Different alphabets correspond to different types of jewels, i.e. a cell denoted by `a` contains a jewel of type A, and a cell denoted by `A` contains a hole to place a jewel of type A. It is said that, when we place a jewel to a corresponding hole, something happy will happen.

At the cells with jewels, you can choose whether you pick a jewel or not. Similarly, at the cells with holes, you can choose whether you place a jewel you have or not. Initially you do not have any jewels. You have a very big bag, so you can bring arbitrarily many jewels. However, your bag is a stack, that is, you can only place the jewel that you picked up last.

On the way from cell (1, 1) to cell (W, H), how many jewels can you place to correct holes?



Input

The input contains a sequence of datasets. The end of the input is indicated by a line containing two zeroes. Each dataset is formatted as follows.


H W
C_{11} C_{12} ... C_{1W}
C_{21} C_{22} ... C_{2W}
...
C_{H1} C_{H2} ... C_{HW}


Here, H and W are the height and width of the grid. You may assume 1 \leq W, H \leq 50. The rest of the datasets consists of H lines, each of which is composed of W letters. Each letter C_{ij} specifies the type of the cell (i, j) as described before. It is guaranteed that C_{11} and C_{WH} are never `#`.

You may also assume that each lowercase or uppercase alphabet appear at most 10 times in each dataset.

Output

For each dataset, output the maximum number of jewels that you can place to corresponding holes. If you cannot reach the cell (W, H), output -1.

Examples

Input

3 3
ac#
b#C
.BA
3 3
aaZ
a#Z
aZZ
3 3
..#
.#.
#..
1 50
abcdefghijklmnopqrstuvwxyYXWVUTSRQPONMLKJIHGFEDCBA
1 50
aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyY
1 50
abcdefghijklmnopqrstuvwxyABCDEFGHIJKLMNOPQRSTUVWXY
1 50
aaaaaaaaaabbbbbbbbbbcccccCCCCCBBBBBBBBBBAAAAAAAAAA
10 10
...#......
a###.#####
.bc...A...
##.#C#d#.#
.#B#.#.###
.#...#e.D.
.#A..###.#
..e.c#..E.
####d###.#
##E...D.C.
0 0


Output

2
0
-1
25
25
1
25
4


Input

3 3
ac#
b#C
.BA
3 3
aaZ
a#Z
aZZ
3 3
..#
.#.
..
1 50
abcdefghijklmnopqrstuvwxyYXWVUTSRQPONMLKJIHGFEDCBA
1 50
aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyY
1 50
abcdefghijklmnopqrstuvwxyABCDEFGHIJKLMNOPQRSTUVWXY
1 50
aaaaaaaaaabbbbbbbbbbcccccCCCCCBBBBBBBBBBAAAAAAAAAA
10 10
...#......
a###.#####
.bc...A...
.#C#d#.#
.#B#.#.###
.#...#e.D.
.#A..###.#
..e.c#..E.
d###.#
E...D.C.
0 0


Output

2
0
-1
25
25
1
25
4

### Response

```cpp
     #include <bits/stdc++.h>

//    #include <boost/multiprecision/cpp_int.hpp>
// #define int long long
 #define inf  1000000007
 #define pa pair<int,int>
 #define ll long long
 #define pal pair<double,double>
 #define ppap pair<pa,int>
  #define PI 3.14159265358979323846
  #define paa pair<int,char>
  #define  mp make_pair
  #define  pb push_back
  #define EPS (1e-10)
                                          
    int dx[8]={0,1,0,-1,1,1,-1,-1};
    int dy[8]={1,0,-1,0,-1,1,1,-1};
                                            using namespace std;
                                   			class pa3{
                                            	public:
                                            	int x,y,z;
                                            	pa3(int x=0,int y=0,int z=0):x(x),y(y),z(z) {}
                                            	bool operator < (const pa3 &p) const{
                                            		if(x!=p.x) return x<p.x;
                                            		if(y!=p.y) return y<p.y;
                                            		 return z<p.z;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                   				bool operator > (const pa3 &p) const{
                                            		if(x!=p.x) return x>p.x;
                                            		if(y!=p.y) return y>p.y;
                                            		 return z>p.z;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa3 &p) const{
                                            		return x==p.x && y==p.y && z==p.z;
                                            	}
                                            		bool operator != (const pa3 &p) const{
                                            			return !( x==p.x && y==p.y && z==p.z);
                                            	}
                                            
                                            };
                                            
                                            class pa4{
                                            	public:
                                            	int x;
                                            	int y,z,w;
                                            	pa4(int x=0,int y=0,int z=0,int w=0):x(x),y(y),z(z),w(w) {}
                                            	bool operator < (const pa4 &p) const{
                                            		if(x!=p.x) return x<p.x;
                                            		if(y!=p.y) return y<p.y;
                                            		if(z!=p.z)return z<p.z;
                                            		return w<p.w;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator > (const pa4 &p) const{
                                            		if(x!=p.x) return x>p.x;
                                            		if(y!=p.y) return y>p.y;
                                            		if(z!=p.z)return z>p.z;
                                            		return w>p.w;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa4 &p) const{
                                            		return x==p.x && y==p.y && z==p.z &&w==p.w;
                                            	}
                                            		
                                            
                                            };
                                            class pa2{
                                            	public:
                                            	int x,y;
                                            	pa2(int x=0,int y=0):x(x),y(y) {}
                                            	pa2 operator + (pa2 p) {return pa2(x+p.x,y+p.y);}
                                            	pa2 operator - (pa2 p) {return pa2(x-p.x,y-p.y);}
                                            	bool operator < (const pa2 &p) const{
                                            		return y != p.y ? y<p.y: x<p.x;
                                            	}
                                            	bool operator > (const pa2 &p) const{
                                            		return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa2 &p) const{
                                            		return abs(x-p.x)==0 && abs(y-p.y)==0;
                                            	}
                                            	bool operator != (const pa2 &p) const{
                                            		return !(abs(x-p.x)==0 && abs(y-p.y)==0);
                                            	}
                                            		
                                            
                                            };
                                            
/*
                                            class Point{
                                            	public:
                                            	double x,y;
                                            	Point(double x=0,double y=0):x(x),y(y) {}
                                            	Point operator + (Point p) {return Point(x+p.x,y+p.y);}
                                            	Point operator - (Point p) {return Point(x-p.x,y-p.y);}
                                            	Point operator * (double a) {return Point(x*a,y*a);}
                                            	Point operator / (double a) {return Point(x/a,y/a);}
                                            	double absv() {return sqrt(norm());}
                                            	double norm() {return x*x+y*y;}
                                            	bool operator < (const Point &p) const{
                                            		return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const Point &p) const{
                                            		return fabs(x-p.x)<EPS && fabs(y-p.y)<EPS;
                                            	}
                                            };
                                            typedef Point Vector;
                                     #define pl pair<int,pas>
                                            struct Segment{
                                            Point p1,p2;
                                            };
                                             double dot(Vector a,Vector b){
                                            	return a.x*b.x+a.y*b.y;
                                            }
                                            double cross(Vector a,Vector b){
                                            	return a.x*b.y-a.y*b.x;
                                            }
                                        
                bool parareru(Point a,Point b,Point c,Point d){
                //	if(abs(cross(a-b,d-c))<EPS)cout<<"dd "<<cross(a-b,d-c)<<endl;
                	return abs(cross(a-b,d-c))<EPS;
                }
                double distance_ls_p(Point a, Point b, Point c) {
                  if ( dot(b-a, c-a) < EPS ) return (c-a).absv();
                  if ( dot(a-b, c-b) < EPS ) return (c-b).absv();
                  return abs(cross(b-a, c-a)) / (b-a).absv();
                }
                bool is_intersected_ls(Segment a,Segment b) {
                	if(a.p1==b.p1||a.p2==b.p1||a.p1==b.p2||a.p2==b.p2) return false;
                	if(parareru((a.p2),(a.p1),(a.p1),(b.p2))&&parareru((a.p2),(a.p1),(a.p1),(b.p1))){
                //		cout<<"sss"<<endl;
                		if(dot(a.p1-b.p1,a.p1-b.p2)<EPS) return true;
                		if(dot(a.p2-b.p1,a.p2-b.p2)<EPS) return true;
                		if(dot(a.p1-b.p1,a.p2-b.p1)<EPS) return true;
                		if(dot(a.p1-b.p2,a.p2-b.p2)<EPS) return true;
                		return false;
                	}
                  else return ( cross(a.p2-a.p1, b.p1-a.p1) * cross(a.p2-a.p1, b.p2-a.p1) < EPS ) && ( cross(b.p2-b.p1, a.p1-b.p1) * cross(b.p2-b.p1, a.p2-b.p1) < EPS );
                }
                 
                double segment_dis(Segment a,Segment b){
                	if(is_intersected_ls(a,b))return 0;
                	double r=distance_ls_p(a.p1, a.p2, b.p1);
                	r=min(r,distance_ls_p(a.p1, a.p2, b.p2));
                	r=min(r,distance_ls_p(b.p1, b.p2, a.p2));
                	r=min(r,distance_ls_p(b.p1, b.p2, a.p1));
                	return r;
                }
                Point intersection_ls(Segment a, Segment b) {
                  Point ba = b.p2-b.p1;
                  double d1 = abs(cross(ba, a.p1-b.p1));
                  double d2 = abs(cross(ba, a.p2-b.p1));
                  double t = d1 / (d1 + d2);
                 
                  return a.p1 + (a.p2-a.p1) * t;
                }
 */                
                                string itos( int i ) {
                                ostringstream s ;
                                s << i ;
                                return s.str() ;
                                }
                                 
                                int gcd(int v,int b){
                                	if(v>b) return gcd(b,v);
                                	if(v==b) return b;
                                	if(b%v==0) return v;
                                	return gcd(v,b%v);
                                }
                 
                                double distans(double x1,double y1,double x2,double y2){
                                	double rr=(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
                                	return sqrt(rr);
                                	
                                }
                                int mod;
int extgcd(int a, int b, int &x, int &y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }
    int d = extgcd(b, a%b, y, x);
    y -= a/b * x;
    return d;
}
    
                                
                int pr[1000010];
                int inv[1000010];
                
                int beki(int wa,int rr,int warukazu){
                	if(rr==0) return 1%warukazu;
                	if(rr==1) return wa%warukazu;
                	wa%=warukazu;
                	if(rr%2==1) return ((ll)beki(wa,rr-1,warukazu)*(ll)wa)%warukazu;
                	ll zx=beki(wa,rr/2,warukazu);
                	return (zx*zx)%warukazu;
                }
    double bekid(double w,int r){
    	if(r==0) return 1.0;
    	if(r==1) return w;
    	if(r%2) return bekid(w,r-1)*w;
    	double f=bekid(w,r/2);
    	return f*f;
    }
                
    			int comb(int nn,int rr){
    				int r=pr[nn]*inv[rr];
    				r%=mod;
    				r*=inv[nn-rr];
    				r%=mod;
    				return r;
    			}
                
                void gya(int ert){
                	pr[0]=1;
                	for(int i=1;i<ert;i++){
                		pr[i]=(pr[i-1]*i)%mod;
                	}
                	for(int i=0;i<ert;i++) inv[i]=beki(pr[i],mod-2,mod);
                	
                }
                
              //   cin.tie(0);
    		//	ios::sync_with_stdio(false);
    			//priority_queue<pa3,vector<pa3>,greater<pa3>> pq;            
                 //sort(ve.begin(),ve.end(),greater<int>());
    
                                     //----------------kokomade tenpure------------

string s[50];
int ka[50][50][50][50];
int ans[50][50][50][50];
vector<pa> ve[26];

int h,w;
int dfs(int i,int j,int x,int y){
//	cout<<i<<" "<<j<<" "<<x<<" "<<y<<endl;
	if(i>x || j>y) return -1;
	if(i<0 || i>=h) return-1;
	if(j<0 || j>=w) return -1;
	if(!ka[i][j][x][y])return -1;
	if(ans[i][j][x][y]>=0) return ans[i][j][x][y];
	if(i==x && j==y ){
		ans[i][j][x][y]=0;
		return 0;
	}
	if(s[i][j]=='.' || (s[i][j]>='A' && s[i][j]<='Z')){
		int r=-1;
		r=max(r,dfs(i+1,j,x,y));
		r=max(r,dfs(i,j+1,x,y));
		ans[i][j][x][y]=r;
		return r;
	}
	{
		assert(s[i][j]>='a' && s[i][j]<='z');
	//	cout<<s[i][j]<<endl;
		int r=-1;
		r=max(r,dfs(i+1,j,x,y));
		r=max(r,dfs(i,j+1,x,y));
		int c=s[i][j]-'a';
		for(auto v:ve[c]){
			if(i<=v.first && v.first<=x && j<=v.second && v.second<=y){
		//		cout<<"  "<<v.first<<" "<<v.second<<endl;
				if(v.first==x && v.second==y && abs(x-i)+abs(y-j)==1){
					r=1;
				}
				else if(v.first==x && v.second==y){
					int f1=-1;
					f1=max(f1,dfs(i+1,j,v.first-1,v.second));
					f1=max(f1,dfs(i+1,j,v.first,v.second-1));
					f1=max(f1,dfs(i,j+1,v.first-1,v.second));
					f1=max(f1,dfs(i,j+1,v.first,v.second-1));
					if(f1>=0) r=max(r,f1+1);
				}
				else{
					if(ka[i][j][v.first][v.second]){
						int f1,f2,f3;
						f1=dfs(i,j,v.first,v.second);
						if(f1<0) continue;
						f2=dfs(v.first+1,v.second,x,y);
						f3=dfs(v.first,v.second+1,x,y);
						f2=max(f2,f3);
						if(f2<0) continue;
						r=max(r,f1+f2);
					}
				}
			}
		}
		ans[i][j][x][y]=r;
		return r;
	}
}

int solve(){

	cin>>h>>w;
	
	if(h==0 && w==0) exit(0);
	for(int i=0;i<26;i++)ve[i].clear();
	for(int i=0;i<50;i++)s[i]="";
	for(int i=0;i<h;i++)cin>>s[i];
	for(int i=0;i<50;i++)for(int j=0;j<50;j++)for(int k=0;k<50;k++)for(int l=0;l<50;l++){
		ka[i][j][k][l]=0;
		ans[i][j][k][l]=-1;
	}
	
	for(int i=0;i<h;i++)for(int j=0;j<w;j++){
		if(s[i][j]!='#' && s[i][j]!='.'){
				if(s[i][j]<='Z')ve[s[i][j]-'A'].pb({i,j});
		}
		if(s[i][j]=='#')continue;
		ka[i][j][i][j]=1;
		for(int x=i;x<h;x++)for(int y=j;y<w;y++)if(s[x][y]!='#'){
			if(x==i && y==j) continue;
			if(x!=i){
				if(ka[i][j][x-1][y])ka[i][j][x][y]=1;
			}
			if(y!=j){
				if(ka[i][j][x][y-1])ka[i][j][x][y]=1;
			}
		}
	}
	
	if(!ka[0][0][h-1][w-1])return -1;
	dfs(0,0,h-1,w-1);
	//for(int i=0;i<w;i++)for(int j=i;j<=w;j++)cout<<i<<" "<<j<<" "<<ans[0][i][0][j]<<endl;
	return dfs(0,0,h-1,w-1);

}

 signed main(){

    	       cin.tie(0);
   			ios::sync_with_stdio(false);

 	while(1){
 		cout<<solve()<<endl;
 	}
 	return 0;
  }



```