import java.util.Scanner;

public class Yukicoder402 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int h = sc.nextInt() + 2, w = sc.nextInt() + 2;
        String[] s = new String[h];
        int[] map = new int[h * w];
        int[] map_buf = 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++) {
            if (i == 0 || i == h - 1) {
                for (int x = 0; x < w; x++) {
                    map[i * w + x] = 0;
                    map_buf[i * w + x] = 0;
                }
            }
            if (i == 0 || i == h - 1) continue;
            s[i] = sc.next();
            for (int x = 0; x < w; x++) {
                if (x == 0 || x == w - 1) {
                    map[i * w + x] = 0;
                    map_buf[i * w + x] = 0;
                } else if (s[i].charAt(x - 1) == '.') {
                    map[i * w + x] = 0;
                    map_buf[i * w + x] = 0;
                } else {
                    map[i * w + x] = 1;
                    map_buf[i * w + x] = 1;
                }
            }
        }

        int cnt, k;
        for (k = 1; k < 1500; k++) {
            cnt = 0;
            for (int y = k; y < h - k; y++) {
                for (int x = k; x < w - k; x++) {
                    if (map[y * w + x] == 1) {
                        for (int p = 0; p < 8; p++) {
                            if (map[(y + dy[p]) * w + (x + dx[p])] == 0) {
                                map_buf[y * w + x] = 0;
                                cnt++;
                                break;
                            }
                        }
                    }
                }
            }
            for (int y = k; y < h - k; y++) {
                for (int x = k; x < w - k; x++) {
/*                    if (map[y * w + x] == 1)
                        System.out.print("#");
                    else
                        System.out.print(".");
        */
                    map[y * w + x] = map_buf[y * w + x];
                }
            }
            if (cnt == 0) break;
        }
        System.out.println(k-1);
    }
}