#pragma GCC optimize ("O3")
#pragma GCC target ("avx")
#include <bits/stdc++.h>
using namespace std;

short h, w, dp[3001];
char g[3001];

int main() {
    cin >> h >> w;
    cin.ignore();
    short ans = 0;
    for (int i = 0; i < h; i++) {
        gets(g);
        // a dp0[i]
        // b dp1[i]
        // x = min(a, b)
        short x = 0;
        for (int j = 0; j < w; j++) {
            short tmp = dp[j];
            dp[j] = g[j] == '.' ? 0 : min(x, dp[j]) + 1;
            x = min(tmp, dp[j]);
            ans = max(ans, dp[j]);
        }
    }
    cout << (ans + 1) / 2 << endl;
}