#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <ctime>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <unordered_set>
#include <cstring>
#include <vector>
#include <algorithm>
#include <functional>
#include <fstream>
#include <sstream>
#include <complex>
#include <bitset>
#include <stack>
#include <queue>
#include <cstring>
#include <numeric>
#include <cassert>
using namespace std;
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rev(i,n) for(int i=(n)-1;(i)>=0;(i)--)
#define all(a) (a).begin(),(a).end()
#define pb(a) push_back(a)
#define bitcount(b) __builtin_popcount(b)
template<typename T, typename S> vector<T>& operator<<(vector<T>& a, S b) { a.push_back(b); return a; }
template<typename T> void operator>>(vector<T>& a, int b) {while(b--)if(!a.empty())a.pop_back();}
bool isprime(int n){ if(n<2)return false;  for(int i=2;i*i<=n;i++)if(n%i==0)return false;  return true;} 

int done[20][20];
char g[20][20];
struct NODE{
	int x,y,c;
};
queue<NODE> Q;
void dfs(int x,int y,int c){
	if( g[y][x] != c ) return;
	if( done[y][x] ) return;
	done[y][x] = true;
	Q.push({x,y,0});
	dfs(x,y-1,c);
	dfs(x+1,y,c);
	dfs(x,y+1,c);
	dfs(x-1,y,c);
}

int main(){
	int H,W;
	cin >> W >> H;
	for(int i = 0 ; i < H ; i++){
		for(int j = 0 ; j < W ; j++){
			cin >> g[i][j];
		}
	}
	int ok = 0;
	for(int i = 0 ; i < H ; i++){
		for(int j = 0 ; j < W ; j++){
			if( g[i][j] == '.' ){
				dfs(j,i,g[i][j]);
				ok = 1;
			}
			if(ok) break;
		}
		if(ok) break;
	}
	int okok[25][25] = {};
	while( Q.size() ){
		auto q = Q.front(); Q.pop();
		if( q.y < 0 || q.x < 0 || q.x >= W || q.y >= H ) continue;

		if( okok[q.y][q.x]++) continue;
		if( g[q.y][q.x] == '.' and done[q.y][q.x] == 0 ){
			cout << q.c - 1 << endl;
			return 0;
		}
		Q.push({q.x,q.y+1,q.c+1});
		Q.push({q.x+1,q.y,q.c+1});
		Q.push({q.x,q.y-1,q.c+1});
		Q.push({q.x-1,q.y,q.c+1});

	}
}