#include <iostream>
#include <stdio.h>
#include <algorithm>
using namespace std;

int W, H;
int map[3010][3010] = { 0 };
char c[3010];

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

int main(void)
{
    cin >> H >> W;
    int M = min(H, W) / 2;

    for (int i = 2; i <= H + 1; i++) {
        scanf("%s", c);
        for (int j = 2; j <= W + 1; j++) {
            if(c[j - 2] == '#') map[i][j] = 1510;
        }
    }

    for (int k = 0; k <= M; k++) {
        for (int i = 1; i <= H + 2; i++) {
            for (int j = 1; j <= W + 2; j++) {
                if (map[i][j] == k) {
                    for (int d = 0; d < 8; d++) {
                        map[i + dy[d]][j + dx[d]] = min(map[i + dy[d]][j + dx[d]], k + 1);
                    }
                }
            }
        }
    }

    int ans = 0;
    for (int i = 2; i <= H + 1; i++) {
        for (int j = 2; j <= W + 1; j++) {
            ans = max(ans, map[i][j]);
        }
    }

    cout << ans << endl;
    return 0;
}