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

short h, w, dp[3001];
char g[3002];

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