#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) for(int i = (n) - 1; (i) >= 0; --i)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
#define MOD LL(1e9 + 7)
#define INF 100000000
using namespace std;
typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PI;

int d[20][20];
int dx[4] = { 1, 0, -1, 0 }, dy[4] = { 0, 1, 0, -1 };

int main() {
	int w, h;
	cin >> w >> h;
	char c[20][20];
	int sx, sy;
	REP(i, h) {
		REP(j, w) {
			d[i][j] = INF;
		}
	}
	REP(i, h) {
		REP(j, w) {
			cin >> c[i][j];
			if (c[i][j] == '.') {
				sy = i; sx = j;
			}
		}
	}
	d[sy][sx] = 0;
	queue<PI> q;
	q.push(make_pair(sy, sx));
	while (!q.empty()) {
		PI t = q.front(); q.pop();
		REP(i, 4) {
			int ny = t.first + dy[i], nx = t.second + dx[i];
			if (ny >= 0 && nx >= 0 && ny < h && nx < w) {
				int a = (c[ny][nx] == '#');
				if (d[t.first][t.second] + a < d[ny][nx]) {
					d[ny][nx] = d[t.first][t.second] + a;
					q.push(make_pair(ny, nx));
				}
			}
		}
	}
	int ans = 0;
	REP(i, h) {
		REP(j, w) {
			if (c[i][j] == '.') ans = max(ans, d[i][j]);
		}
	}
	cout << ans << endl;
	return 0;
}