#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <sstream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <numeric>
#include <cctype>
#include <tuple>
#include <array>
#include <climits>
#include <bitset>
#include <cassert>
#include <unordered_map>

#ifdef _MSC_VER
#include <agents.h>
#endif

#define FOR(i, a, b) for(int i = (a); i < (int)(b); ++i)
#define rep(i, n) FOR(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define REV(v) v.rbegin(), v.rend()
#define MEMSET(v, s) memset(v, s, sizeof(v))
#define UNIQUE(v) (v).erase(unique(ALL(v)), (v).end())
#define MP make_pair
#define MT make_tuple

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> P;

const int N = 404;
int dist[N][N];

int w, h;
int f(int i, int j){
	return i*w + j;
}

P g(int x){
	return MP(x / w, x % w);
}

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

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout.setf(ios::fixed);
	cout.precision(20);

	cin >> w >> h;
	vector<string> a(h);
	rep(i, h) cin >> a[i];

	int n = w*h;
	rep(i, n) rep(j, n) dist[i][j] = i == j ? 0 : 1e9;

	rep(i, h) rep(j, w){
		rep(d, 4){
			int ni = i + dy[d], nj = j + dx[d];
			if (ni < 0 || ni >= h || nj < 0 || nj >= w) continue;
			int c = a[i][j] == '#' || a[ni][nj] == '#';
			int x = f(i, j), y = f(ni, nj);
			dist[x][y] = dist[y][x] = c;
		}
	}

	rep(i, n) rep(j, n) rep(k, n) dist[j][k] = min(dist[j][k], dist[j][i] + dist[i][k]);

	int ans = 1e9;
	rep(i, h) rep(j, w) rep(k, h) rep(l, w){
		if (a[i][j] == '#' || a[k][l] == '#') continue;
		int x = f(i, j), y = f(k, l);
		if (dist[x][y]) ans = min(ans, dist[x][y] - 1);
	}
	cout << ans << endl;
}