#include <iostream>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>	// require sort next_permutation count __gcd reverse etc.
#include <cstdlib>	// require abs exit atof atoi 
#include <cstdio>		// require scanf printf
#include <functional>
#include <numeric>	// require accumulate
#include <cmath>		// require fabs
#include <climits>
#include <limits>
#include <cfloat>
#include <iomanip>	// require setw
#include <sstream>	// require stringstream 
#include <cstring>	// require memset
#include <cctype>		// require tolower, toupper
#include <fstream>	// require freopen
#include <ctime>		// require srand
#define rep(i,n) for(int i=0;i<(n);i++)
#define ALL(A) A.begin(), A.end()
#define INF 1<<10

using namespace std;

typedef long long ll;
typedef pair<int, int> P;
typedef pair<P, int> PI;

const int dr[4] = {-1, 0, 1, 0 };
const int dc[4] = { 0, 1, 0,-1 };

int W, H;
char cave[22][22];
int used[22][22];

void dfs (int r, int c, char ch1, char ch2 ){ // 現在位置 (r, c ) 通過可能文字 ch1 上書き文字 ch2 

	cave[r][c] = ch2;
	rep (k, 4 ){
		int nr = r + dr[k];
		int nc = c + dc[k];
		if (nr < 0 || nr >= H || nc < 0 || nc >= W ) continue;
		if (cave[nr][nc] != ch1 ) continue;
		dfs (nr, nc, ch1, ch2 );
	} // end rep
}

int bfs (int r, int c, char ch1, char ch2 ){	// 現在位置 (r, c ) 通過可能文字 ch1 探索文字 ch2 
	memset (used, -1, sizeof (used ) );
	used[r][c] = 0;
	queue<PI> que;
	que.push (PI(P (r, c ), 0 ) );

	while (!que.empty() ){
		PI curr = que.front(); que.pop();
		int cr = curr.first.first;
		int cc = curr.first.second;
		int cn = curr.second;
		used[cr][cc] = cn;
		rep (k, 4 ){
			int nr = cr + dr[k];
			int nc = cc + dc[k];
			if (nr < 0 || nr >= H || nc < 0 || nc >= W ) continue;
			if (cave[nr][nc] == ch2 ) return cn;
			if (cave[nr][nc] != ch1 && cave[nr][nc] != '1' ) continue;
			if (used[nr][nc] == -1 || used[nr][nc] > used[r][c] + 1 ){
				que.push (PI( P (nr, nc ), cn + 1 ) );
			} // end if
		} // end rep
	} // end while

	return -1;
} 	

void disp_cave (void ){
	rep (i, H ){
		rep (j, W ){
			cerr << cave[i][j];
		} // end rep
		cerr << endl;
	} // end rep
}

void disp_used (void ){
	cerr << endl;
	rep (i, H ){
		rep (j, W ){
			cerr << setw(2) << used[i][j];
		} // end rep
		cerr << endl;
	} // end rep
}

int main()
{
	memset (cave, 0, sizeof (cave ) );
	ios_base::sync_with_stdio(0);
	cin >> W >> H;
	rep (i, H ) rep (j, W ) cin >> cave[i][j];
	int cnt = 0;
	rep (i, H ) rep (j, W )
		if (cave[i][j] == '.' ){
			dfs (i, j, '.', (char)('1'+cnt) );
			cnt++;
		} // end if			
//	disp_cave ();

	int res = INF;
	rep (i, H ) rep (j, W ) if (cave[i][j] == '1' ){
		int curr = bfs (i, j, '#', '2' );
		res = min (res, curr );
//		disp_used ();
	} // end if
	cout << res << endl;

	return 0;
}