using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;



class Program
{
    public void Proc()
    {
        Reader.IsDebug = false;
        int[] inpt = Reader.ReadLine().Split(' ').Select(a=>int.Parse(a)).ToArray();

        int H = inpt[0];
        int W = inpt[1];

        Dictionary<int, Dictionary<int, int>> step = new Dictionary<int, Dictionary<int, int>>();

        char[,] map = new char[H, W];

        for(int i=0; i<H; i++) {
            if(!step.ContainsKey(i)) {
                step.Add(i, new Dictionary<int, int>());
            }
            string tmp = Reader.ReadLine();
            for(int j=0; j<tmp.Length; j++) {
                map[i,j] = tmp[j];
                if(tmp[j] == '.') {
                    step[i][j] = 0;
                }
                else if(i==0 || i == H-1 || j == 0 || j == W-1) {
                    step[i][j] = 1;
                }
            }
        }
        for(int i=0; i<=H*W/4; i++) {
            int[] yKeys = step.Where(a=>a.Value.Count(b=>b.Value == i) > 0).Select(a=>a.Key).ToArray();

            yKeys.ToList().ForEach(a=>{
                step[a].Where(b=>b.Value == i).ToList().ForEach(b=>{
                    for(int j=Math.Max(0, a-1); j<=Math.Min(H-1, a+1); j++) {
                        for(int k=Math.Max(0, b.Key - 1); k<=Math.Min(W-1, b.Key+1); k++) {
                            if((!step[j].ContainsKey(k)) && map[j,k] == '#')  {
                                step[j][k] = i+1;
                            }
                        }
                    } 
                });
            });

        }

        int ans = step.Max(a=>a.Value.Max(b=>b.Value));
        Console.WriteLine(ans);



    }


    public class Reader
    {
        public static bool IsDebug = true;
        private static String PlainInput = @"

8 8
.#..#...
.######.
#####...
#####.#.
########
######.#
#####...
...####.


";
        private static System.IO.StringReader Sr = null;
        public static string ReadLine()
        {
            if (IsDebug)
            {
                if (Sr == null)
                {
                    Sr = new System.IO.StringReader(PlainInput.Trim());
                }
                return Sr.ReadLine();
            }
            else
            {
                return Console.ReadLine();
            }
        }
    }
    static void Main()
    {
        Program prg = new Program();
        prg.Proc();
    }
}