You've gotten an n × m sheet of squared paper. Some of its squares are painted. Let's mark the set of all painted squares as A. Set A is connected. Your task is to find the minimum number of squares that we can delete from set A to make it not connected.

A set of painted squares is called connected, if for every two squares a and b from this set there is a sequence of squares from the set, beginning in a and ending in b, such that in this sequence any square, except for the last one, shares a common side with the square that follows next in the sequence. An empty set and a set consisting of exactly one square are connected by definition.

Input

The first input line contains two space-separated integers n and m (1 ≤ n, m ≤ 50) — the sizes of the sheet of paper. 

Each of the next n lines contains m characters — the description of the sheet of paper: the j-th character of the i-th line equals either "#", if the corresponding square is painted (belongs to set A), or equals "." if the corresponding square is not painted (does not belong to set A). It is guaranteed that the set of all painted squares A is connected and isn't empty.

Output

On the first line print the minimum number of squares that need to be deleted to make set A not connected. If it is impossible, print -1. 

Examples

Input

5 4
####
#..#
#..#
#..#
####


Output

2


Input

5 5
#####
#...#
#####
#...#
#####


Output

2

Note

In the first sample you can delete any two squares that do not share a side. After that the set of painted squares is not connected anymore.

The note to the second sample is shown on the figure below. To the left there is a picture of the initial set of squares. To the right there is a set with deleted squares. The deleted squares are marked with crosses. 

<image>
import java.awt.Point;
import java.io.*;
import java.math.BigInteger;
import java.util.*;
import static java.lang.Math.*;
 
public class C {
        
        final boolean ONLINE_JUDGE = System.getProperty("ONLINE_JUDGE")!=null;
        BufferedReader in;
        PrintWriter out;
        StringTokenizer tok = new StringTokenizer("");
        
        void init() throws FileNotFoundException{
                if (ONLINE_JUDGE){
                        in = new BufferedReader(new InputStreamReader(System.in));
                        out = new PrintWriter(System.out);
                }else{
                        in = new BufferedReader(new FileReader("input.txt"));
                        out = new PrintWriter("output.txt");
                }
        }
        
        String readString() throws IOException{
                while(!tok.hasMoreTokens()){
                        tok = new StringTokenizer(in.readLine());
                }
                return tok.nextToken();
        }
        
        int readInt() throws IOException{
                return Integer.parseInt(readString());
        }
        
        long readLong() throws IOException{
                return Long.parseLong(readString());
        }
        
        double readDouble() throws IOException{
                return Double.parseDouble(readString());
        }
        
        int[] readArr(int n) throws IOException{
        	int[] res = new int[n];
        	for(int i = 0; i < n; i++){
        		res[i] = readInt();
        	}
        	return res;
        }
        
        long[] readArrL(int n) throws IOException{
        	long[] res = new long[n];
        	for(int i = 0; i < n; i++){
        		res[i] = readLong();
        	}
        	return res;
        }
        
        public static void main(String[] args){
                new C().run();
        }
        
        public void run(){
                try{
                        long t1 = System.currentTimeMillis();
                        init();
                        solve();
                        out.close();
                        long t2 = System.currentTimeMillis();
                        System.err.println("Time = "+(t2-t1));
                }catch (Exception e){
                        e.printStackTrace(System.err);
                        System.exit(-1);
                }
        }        
        
        void solve() throws IOException{
        	int n = readInt();
        	int m = readInt();
        	b = new boolean[n+2][m+2];
        	int count = 0;
        	for(int i = 0; i < n; i++){
        		char[] c = readString().toCharArray();
        		for(int j = 0; j < m; j++){
        			if(c[j] == '#'){
        				b[i+1][j+1] = true;
        				x = i+1;
        				y = j+1;
        				count++;
        			}
        		}
        	}
        	
        	if(count <= 2){
        		out.println(-1);
        		return;
        	}
        	
        	for(int i = 1; i <= n; i++){
        		for(int j = 1; j <= m; j++){
        			if(b[i][j]){
        				b[i][j] = false;
        				used = new boolean[n+2][m+2];
        				if(x == i && y == j){
        					if(b[i-1][j]) x = i-1;
        					else if(b[i][j-1]) y = j-1;
        				}
        				dfs(x,y);
        				for(int i1 = 1; i1 <= n; i1++){
        					for(int j1 = 1; j1 <= m; j1++){
        						if(b[i1][j1] && !used[i1][j1]){
        							out.println(1);
        							return;
        						}
        					}
        				}
        				b[i][j] = true;
        			}
        		}
        	}
        	out.println(2);
        }
        
        
        boolean[][] b;
        int x,y;
        
        boolean[][] used;
        
        void dfs(int o, int p){
        	used[o][p] = true;
        	if(b[o-1][p] && !used[o-1][p])
        		dfs(o-1,p);
        	if(b[o+1][p] && !used[o+1][p])
        		dfs(o+1,p);
        	if(b[o][p-1] && !used[o][p-1])
        		dfs(o,p-1);
        	if(b[o][p+1] && !used[o][p+1])
        		dfs(o,p+1);
        }
        
        void maxHepify(int[] a, int i, int length){
        	int l = (i<<1) + 1;
        	int r = (i<<1) + 2;
        	int largest = i;
        	if(l < length && a[l] > a[largest])
        		largest = l;
        	if(r < length && a[r] > a[largest])
        		largest = r;
        	if(largest != i){
        		a[largest] += a[i];
        		a[i] = a[largest] - a[i];
        		a[largest] -= a[i];
        		maxHepify(a, largest, length);
        	}
        }
        
        void buildMaxHeap(int[] a){
        	for(int i = a.length/2 - 1; i >= 0; i--){
        		maxHepify(a, i, a.length);
        	}
        }
        
        void heapSort(int[] a){
        	buildMaxHeap(a);
        	for(int i = a.length - 1; i > 0; i--){
        		a[i] += a[0];
        		a[0] = a[i] - a[0];
        		a[i] -= a[0];
        		maxHepify(a, 0, i);
        	}
        }

        
        int[] zFunction(char[] s){
        	int[] z = new int[s.length];
        	z[0] = 0;
        	for (int i=1, l=0, r=0; i<s.length; ++i) {
        		if (i <= r)
        			z[i] = min (r-i+1, z[i-l]);
        		while (i+z[i] < s.length && s[z[i]] == s[i+z[i]])
        			++z[i];
        		if (i+z[i]-1 > r){
        			l = i; 
        			r = i+z[i]-1;
        		}
        	}	
        	return z;
        }
        
        int[] prefixFunction(char[] s){
        	int[] pr = new int[s.length];
        	for (int i = 1; i< s.length; ++i) {
        		int j = pr[i-1];
        		while (j > 0 && s[i] != s[j])
        			j = pr[j-1];
        		if (s[i] == s[j])  ++j;
        		pr[i] = j;
        	}
        	return pr;
        }
        
        int ModExp(int a, int n, int mod){
        	int res = 1;
        	while (n!=0)
        		if ((n & 1) != 0) {
        			res = (res*a)%mod;
        			--n;
        		}
        		else {
        			a = (a*a)%mod;
        			n >>= 1;
        		}
        	return res;
        }
        
        
        public static class Utils {       	
 
        	private Utils() {}

        	public static void mergeSort(int[] a) {
                    mergeSort(a, 0, a.length - 1);
            }
             
        	private static void mergeSort(int[] a, int leftIndex, int rightIndex) {
                    final int MAGIC_VALUE = 50;
                    if (leftIndex < rightIndex) {
                            if (rightIndex - leftIndex <= MAGIC_VALUE) {
                                    insertionSort(a, leftIndex, rightIndex);
                            } else {
                                    int middleIndex = (leftIndex + rightIndex) / 2;
                                    mergeSort(a, leftIndex, middleIndex);
                                    mergeSort(a, middleIndex + 1, rightIndex);
                                    merge(a, leftIndex, middleIndex, rightIndex);
                            }
                    }
            }
 
            private static void merge(int[] a, int leftIndex, int middleIndex, int rightIndex) {
            	int length1 = middleIndex - leftIndex + 1;
            	int length2 = rightIndex - middleIndex;
                int[] leftArray = new int[length1];
                int[] rightArray = new int[length2];
                System.arraycopy(a, leftIndex, leftArray, 0, length1);
                System.arraycopy(a, middleIndex + 1, rightArray, 0, length2);
                for (int k = leftIndex, i = 0, j = 0; k <= rightIndex; k++) {
                    if (i == length1) {
                            a[k] = rightArray[j++];
                    } else if (j == length2) {
                            a[k] = leftArray[i++];
                    } else {
                            a[k] = leftArray[i] <= rightArray[j] ? leftArray[i++] : rightArray[j++];
                    }
                }
            }
 
            private static void insertionSort(int[] a, int leftIndex, int rightIndex) {
                for (int i = leftIndex + 1; i <= rightIndex; i++) {
            		int current = a[i];
                    int j = i - 1;
                	while (j >= leftIndex && a[j] > current) {
                        a[j + 1] = a[j];
                        j--;
                        }
                    a[j + 1] = current;
                }
            }
        }
        
         
       
        
        boolean isPrime(int a){
        	for(int i = 2; i <= sqrt(a); i++)
        		if(a % i == 0) return false;
        	return true;
        }
        
        static double distance(long x1, long y1, long x2, long y2){
        	return Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
        }
        
        static long gcd(long a, long b){
        	if(min(a,b) == 0) return max(a,b);
        	return gcd(max(a, b) % min(a,b), min(a,b));
        }
        
        static long lcm(long a, long b){
        	return a * b /gcd(a, b);
        }
}

/*class Treap<K extends Comparable<K>>{
	
	public K x;
	public double y;
	public Treap<K> left;
	public Treap<K> right;
	
	public Treap(K x, double y, Treap<K> left, Treap<K> right) {
		this.x = x;
		this.y = y;
		this.left = left;
		this.right = right;
	}
	
	public static <K extends Comparable<K>> Treap<K> merge(Treap<K> l, Treap<K> r){
		if(l == null) return r;
		if(r == null) return l;
		if(l.y > r.y){
			return new Treap<K>(l.x, l.y, l.left, merge(l.right, r));
		}
		else{
			return new Treap<K>(r.x, r.y, merge(l, r.left), r.right);
		}
	}
	
	public void split(K x, Treap<K> left, Treap<K> right){
		Treap<K> newTreap = null;
		if(this.x.compareTo(x) <= 0){
			if(this.right == null){
				right = null;
			}
			else{
				right.split(x, newTreap, right);
			}
			left = new Treap<K>(this.x, this.y, left, newTreap);
		}
		else{
			if(this.left == null){
				left = null;
			}
			else{
				left.split(x, left, newTreap);
			}
			right = new Treap<K>(x, y, newTreap, right);
		}
	}
	
	public Treap<K> add(K x){
		Treap<K> left = null, right = null;
		this.split(x, left, right);
		Treap<K> temp = new Treap<K>(x, random(), null, null);
		return merge(merge(left, temp), right);
	}
	
	@SuppressWarnings("null")
	public Treap<K> remove(K x){
		Treap<K> left = null, temp = null, right = null;
		this.split(x, left, right);
		right.split(x, temp, right);
		return merge(left, right);
	}
	
	public static <K extends Comparable<K>> Treap<K> build(K[] a){
		Treap<K> temp = new Treap<K>(a[0], random(), null, null);
		for(int i = 1; i < a.length; i++){
			temp = temp.add(a[i]);
		}
		return temp;
	}
}*/