Time Limit: 8 sec / Memory Limit: 64 MB





Example

Input

10 10
.....#....
.....#....
.....#....
######....
..........
####......
....###...
t..#..####
...##.....
....#...##
3
0 3
0 5
4 6


Output

2
#include <iostream>
#include <cstdio>
#include <iomanip>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <bitset>
#include <stack>
#include <utility>
#include <numeric>
#include <algorithm>
#include <functional>
#include <cctype>
#include <complex>
#include <string>
#include <sstream>
#include <cassert>
using namespace std;

//common
#define BR "\n"

#define ALL(c) (c).begin(),(c).end()
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define EACH(it,o) for(auto it = (o).begin(); it != (o).end(); ++it)
#define IN(l,v,r) ((l)<=(v) && (v)<(r))

typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii;
typedef long long ll; typedef vector<long long> vl; typedef pair<long long,long long> pll; typedef vector<pair<long long,long long> > vpll;
typedef vector<string> vs; typedef long double ld;

//debug
#ifdef NDEBUG
#define DUMP(x)
#define DUMPLN(x)
#define DEBUG(x)
#define DEBUGLN(x)
#define LINE()
#define LINELN()
#define CHECK(exp,act)
#define STOP(e)
#else
#define DUMP(x)  cerr << #x << " = " << (x)
#define DUMPLN(x)  DUMP(x) <<endl
#define DEBUG(x) DUMP(x) << LINE() << " " << __FILE__
#define DEBUGLN(x) DEBUG(x)<<endl
#define LINE()    cerr<< " (L" << __LINE__ << ")"
#define LINELN()    LINE()<<endl
#define CHECK(exp,act)  if(exp!=act){DUMPLN(exp);DEBUGLN(act);}
#define STOP(e)  CHECK(e,true);if(!(e)) exit(1);
#endif

template<class T> inline string toString(const vector<T>& x) {
	stringstream ss;
	REP(i,x.size()){
		if(i!=0)ss<<" ";
		ss<< x[i];
	}
	return ss.str();
}
template<class T> inline string toString(const vector<vector<T>>& map) {
	stringstream ss;
	REP(i,map.size()){
		if(i!=0)ss<<BR;
		ss<< toString(map[i]);
	}
	return ss.str();
}
template<class K,class V>  string toString(map<K,V>& x) {
	string res;stringstream ss;
	for(auto& p:x)ss<< p.first<<":" << p.second<<" ";
	return ss.str();
}

template<typename T,typename V> inline T mod(T v,V MOD){
	return (v%MOD+MOD)%MOD;
}

struct UnionFind{
    vector<int> par; // 親
    vector<int> rank; // 木の深さ
    int size;
    UnionFind(int n){
        REP(i,n) par.push_back(i);
        rank = vector<int>(n);
        size=n;
    }
    int root(int x){
        if(par[x] == x)return x;
        return par[x] = root(par[x]);
    }
    bool same(int x,int y){
        return root(x) == root(y);
    }
    void unite(int x,int y){
        x = root(x);y = root(y);
        if(x==y)return;
        if(rank[x] < rank[y])par[x] = y;
        else par[y] = x;
        if(rank[x] == rank[y]) rank[x]++;
        size--;
    }
};

int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};

int INF=1<<28;

int H,W;
int enc(int y,int x){
	return y*W+x;
}
int main(){
	cin >> W >> H;
	vector<string> map(H);REP(y,H)cin >> map[y];
	int N;cin >> N;
	vector<int> xs(N),ys(N);REP(i,N)cin >> xs[i] >> ys[i];

	int tx,ty;
	REP(y,H)REP(x,W){
		if(map[y][x]=='t'){
			tx=x;ty=y;
		}
	}

	UnionFind uf(H*W);
	REP(y,H)REP(x,W){
		if(map[y][x]=='#')continue;
		REP(di,4){
			int nx=x+dx[di],ny=y+dy[di];
			if(!IN(0,nx,W) || !IN(0,ny,H))continue;
			if(map[ny][nx]=='#')continue;
			uf.unite(enc(y,x), enc(ny,nx));
		}
	}

	int time=0;
	while(!uf.same(enc(ty,tx),enc(0,0))){
		time++;
		if(time-1==N)break;
		int x=xs[time-1],y=ys[time-1];
		if(!IN(0,x,W) || !IN(0,y,H))continue;
		map[y][x]='.';
		REP(di,4){
			int nx=x+dx[di],ny=y+dy[di];
			if(!IN(0,nx,W) || !IN(0,ny,H))continue;
			if(map[ny][nx]=='#')continue;
			uf.unite(enc(y,x),enc(ny,nx));
		}
	}
	cout<< (time!=N+1?time:-1) <<endl;
	return 0;
}