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];

        int[,] step = new int[H, W];

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

        Queue<int[]> q = new Queue<int[]>();
        for(int i=0; i<H; i++) {
            string tmp = Reader.ReadLine();
            for(int j=0; j<tmp.Length; j++) {
                map[i,j] = tmp[j];
                if(tmp[j] == '.') {
                    int[] t = new int[]{i, j, 0};
                    q.Enqueue(t);
                }
                else if(i==0 || i == H-1 || j == 0 || j == W-1) {
                    int[] t = new int[]{i, j, 1};
                    q.Enqueue(t);
                }
            }
        }
        while (q.Count > 0)
        {
            int[] task = q.Dequeue();
            int posY = task[0];
            int posX = task[1];
            int cnt = task[2];

            if((step[posY, posX] == 0 && map[posY, posX] == '#') || (cnt == 0 && map[posY , posX] == '.')) {
                step[posY, posX] = cnt;
                for(int i = Math.Max(0, posY-1); i<= Math.Min(H-1, posY+1); i++) {
                    for(int j=Math.Max(0, posX - 1); j<= Math.Min(W-1, posX+1); j++) {
                        if(i==posY && j == posX) {
                            continue;
                        }
                        if(map[i,j] == '#' ) {
                            int[] newT = new int[]{i,j, cnt+1};
                            q.Enqueue(newT);
                        }
                    }
                }
            }
        }

        int ans = 0;
        for(int i=0; i<H; i++) {
            for(int j=0; j<W; j++) {
                ans = Math.Max(ans, step[i,j]);
            }
        }
        Console.WriteLine(ans);



    }


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

7 7
#######
#######
#######
#######
#.#####
#..####
#######


";
        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();
    }
}