using System;
using System.Runtime.Serialization.Formatters.Binary;
using System.Runtime;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
class Program {
    static int H, W;
    static int[,] S;
    static int[] tate = { -1, 0, 1, -1, 1, -1, 0, 1 }, yoko = { -1, -1, -1, 0, 0, 1, 1, 1 };
    static void Main() {
        int[] q = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
        H = q[0];
        W = q[1];
        Queue<XY> Q = new Queue<XY>();
        S = new int[H + 2, W + 2];
        for (int i = 0; i < W + 2; i++) {
            S[0, i] = 0;
            Q.Enqueue(new XY(0, i));
            S[H + 1, i] = 0;
            Q.Enqueue(new XY(H + 1, i));
        }
        for (int i = 0; i < H; i++) {
            string qw = Console.ReadLine();
            for (int j = 0; j < W + 2; j++) {
                if (j == 0 || j == W + 1 || qw[j - 1] == '.') {
                    S[i + 1, j] = 0;
                    Q.Enqueue(new XY(i + 1, j));
                }
                else {
                    S[i + 1, j] = -1;
                }
            }
        }
        while (Q.Count > 0) {
            XY xy = Q.Dequeue();
            for(int i = 0; i < 8; i++) {
                if (tate[i] + xy.Y >= 0 && tate[i] + xy.Y <= H + 1 && yoko[i] + xy.X >= 0 && yoko[i]+xy.X <= W + 1) {
                    if (S[tate[i] + xy.Y, yoko[i] + xy.X] == -1) {
                        S[tate[i] + xy.Y, yoko[i] + xy.X] = S[xy.Y, xy.X] + 1;
                        Q.Enqueue(new XY(tate[i] + xy.Y, yoko[i] + xy.X));
                    }
                }
            }
        }
        int max = int.MinValue;
        for(int i= 1;i<= H; i++) {
            for(int j = 1; j <= W; j++) {
                max = Math.Max(max, S[i, j]);
            }
        }
        Console.WriteLine(max);
    }
}
public struct XY {
    public XY(int y,int x) {
       this.X = x;
        this.Y = y;
    }
  
    public int Y { get; set; }
    public int X { get; set; }
}