import java.util.Scanner;

public class Yukicoder402 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int h = sc.nextInt(), w = sc.nextInt();
        String[] s = new String[h];
        int[] map = new int[h * w];
        int[] dx = {-1, 0, 1, -1, 1, -1, 0, 1};
        int[] dy = {-1, -1, -1, 0, 0, 1, 1, 1};
        for (int i = 0; i < h; i++) {
            s[i] = sc.next();
            for (int x = 0; x < w; x++) {
                if (s[i].charAt(x) == '.') {
                    map[i * w + x] = 0;
                } else {
                    map[i * w + x] = 1;
                }
            }
        }

        int min, max = -1;
        for (int k = 1; k < 1500; k++) {
            for (int y = k; y < h - k; y++) {
                for (int x = k; x < w - k; x++) {
                    if (map[y * w + x] != 0) {
                        min = map[(y + dy[0]) * w + (x + dx[0])];
                        for (int p = 1; p < 8; p++) {
                            min = Math.min(min, map[(y + dy[p]) * w + (x + dx[p])]);
                        }
                        map[y * w + x] = min + 1;
                        max = Math.max(max, map[y * w + x]);
                    }
                }
            }
        }
        System.out.println(max);
    }
}