using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Convert;
using static System.Math;
//using Debug;
//using static System.Globalization.CultureInfo;
using System.Text;
class Program
{
    static void Main(string[] args)
    {
        Solve();
        //WriteLine(Solve());
    }
    static void Solve()
    {
        var hw = Input.ar;
        var gred = Input.gred(hw[0]);
        var que = new Queue<Pair<int, int>>();
        var dist = Enumerable.Repeat(0, hw[0]).Select(_ => Enumerable.Repeat(int.MaxValue, hw[1]).ToArray()).ToArray();
        for (var i = 0; i < hw[0]; i++)
            for (var j = 0; j < hw[1]; j++)
                if (gred[i][j] == '#')
                {
                    dist[i][j] = 0;
                    que.Enqueue(new Pair<int, int>(i, j));
                }
        var gh = new[] { 0, 0, 1, -1 };
        var gw = new[] { 1, -1, 0, 0 };
        while (que.Count != 0)
        {
            var p = que.Dequeue();
            for(var i = 0; i < 4; i++)
            {
                var h = gh[i] + p.v1;
                var w = gw[i] + p.v2;
                if (!Search.IsInside(h, w, hw)||dist[h][w]<=dist[p.v1][p.v2]+1) continue;
                dist[h][w] = dist[p.v1][p.v2] + 1;
                que.Enqueue(new Pair<int, int>(h, w));
            }
        }
        var max = 0;
        for (var i = 0; i < hw[0]; i++)
            for (var j = 0; j < hw[1]; j++)
                max = Max(max, dist[i][j]);
        WriteLine(max);
    }
}

public class Input
{
    public static string read => ReadLine().Trim();
    public  static int[] ar => Array.ConvertAll(read.Split(' '), int.Parse);
    public  static int num => ToInt32(read);
    public static long[] arL => Array.ConvertAll(read.Split(' '), long.Parse);
    public  static long numL => ToInt64(read);
    public static char[][] gred(int h) 
        => Enumerable.Repeat(0, h).Select(v => read.ToCharArray()).ToArray();
    public static int[][] ar2D(int num)
        => Enumerable.Repeat(0, num).Select(_ => ar).ToArray();
    public static long[][] arL2D(int num)
        => Enumerable.Repeat(0, num).Select(_ => arL).ToArray();
    public static T getValue<T>(string g)
    {
        var t = typeof(T);
        if (t == typeof(int))
            return (T)(object)int.Parse(g);
        if (t == typeof(long))
            return (T)(object)long.Parse(g);
        if (t == typeof(string))
            return (T)(object)g;
        if (t == typeof(char))
            return (T)(object)char.Parse(g);
        if (t == typeof(double))
            return (T)(object)double.Parse(g);
        if (t == typeof(bool))
            return (T)(object)bool.Parse(g);
        return default(T);
    }
    public const long Inf = (long)1e18;
    public const double eps = 1e-6;
    public  const string alfa = "abcdefghijklmnopqrstuvwxyz";
    public  const int MOD = 1000000007;
}

public class Search
{
    public static int UpperBound<T>(T[] array,T value)
        where T:IComparable<T>
    {
        var low = 0;
        var high = array.Length;
        while (high > low)
        {
            var mid = (high + low) / 2;
            if (array[mid].CompareTo(value) == 1) high = mid;
            else low = mid + 1;
        }
        return low;
    }

    public static int LowerBound<T>(T[] array,T value)
        where T : IComparable<T>
    {
        var low = 0;
        var high = array.Length;
        while (high > low)
        {
            var mid = (high + low) / 2;
            if (array[mid].CompareTo(value) != -1) high = mid;
            else low = mid + 1;
        }
        return low;
    }

    public static T Max<T>(params T[] array)
        => array.Max();
    public static T Min<T>(params T[] array)
        => array.Min();
    public static bool IsInside(int h, int w, int[] hw)
        => 0 <= h && h < hw[0] && 0 <= w && w < hw[1];
    public static bool IsPrime(long num)
    {
        if (num % 2 == 0 || num == 1) return num == 2;
        for (var i = 3; i * i <= num; i += 2)
            if (num % i == 0) return false;
        return true;
    }
}
public class Pair<T1, T2> : IComparable<Pair<T1, T2>>
{
    public T1 v1 { get; set; }
    public T2 v2 { get; set; }
    public Pair() : this(default(T1), default(T2)) { }
    public Pair(T1 v1, T2 v2)
    { SetValue(v1, v2); }

    public int CompareTo(Pair<T1, T2> p)
    {
        var c = Comparer<T1>.Default.Compare(v1, p.v1);
        if (c == 0)
            c = Comparer<T2>.Default.Compare(v2, p.v2);
        return c;
    }
    public void SetValue(T1 v1,T2 v2) { this.v1 = v1;this.v2 = v2; }
    public static Pair<T1, T2> makePair()
    {
        var r = ReadLine().Split(' ');
        return new Pair<T1, T2>(Input.getValue<T1>(r[0]), Input.getValue<T2>(r[1]));
    }
    public override string ToString()
        => $"{v1.ToString()} {v2.ToString()}";
}



Measured memory_bytes: 56340