#include <iostream>
#include <vector>

int main() {
    using namespace std;
    int h, w;
    cin >> h >> w;
    vector<string> s(h);
    for (auto &e : s) { cin >> e; }

    vector dp(h + 1, vector<int>(w + 1, 0));
    int ans = 0;
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            if (s[i][j] == '.') { continue; }
            dp[i + 1][j + 1] = h;
            dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i + 1][j] + 1);
            dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j + 1] + 1);
            dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j] + 1);
            ans = max(ans, dp[i + 1][j + 1]);
        }
    }
    cout << (ans + 1) / 2 << endl;
}