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

namespace AtCoderWorkspace
{
    class Program
    {
        static void Main(string[] args)
        {
            var cin = new Scanner();
            var H = cin.nextInt();
            var W = cin.nextInt();
            string[] field = new string[H];
            for (int i = 0; i < H; i++)
            {
                field[i] = cin.next();
            }

            Queue<Tuple<int, int>> q = new Queue<Tuple<int, int>>();

            int[,] ifield = new int[H, W];
            int visit = -1;
            for (int i = 0; i < H; i++)
            {
                for (int j = 0; j < W; j++)
                {
                    if (field[i][j] == '#')
                    {
                        ifield[i, j] = 0;
                        q.Enqueue(Tuple.Create(i, j));
                    }
                    else ifield[i, j] = visit;
                }
            }

            int[] vy = { 1, 0, -1, 0 };
            int[] vx = { 0, 1, 0, -1 };

            while (q.Count > 0)
            {
                var now = q.Dequeue();
                int y = now.Item1;
                int x = now.Item2;
                for (int k = 0; k < vy.Length; k++)
                {
                    int ny = y + vy[k];
                    int nx = x + vx[k];
                    if (!(ny >= 0 && nx >= 0 && ny < H && nx < W)) continue;
                    if (ifield[ny, nx] != visit) continue;

                    ifield[ny, nx] = ifield[y, x] + 1;

                    q.Enqueue(Tuple.Create(ny, nx));
                }
            }

            var result = Math.Max(0, ifield.Cast<int>().ToArray().Max()); 
            Console.WriteLine(result);
        }
    }
    
    class Scanner
    {
        string[] s;
        int i;

        char[] cs = new char[] { ' ' };

        public Scanner()
        {
            s = new string[0];
            i = 0;
        }

        public string next()
        {
            if (i < s.Length) return s[i++];
            string st = Console.ReadLine();
            while (st == "") st = Console.ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            if (s.Length == 0) return next();
            i = 0;
            return s[i++];
        }

        public int nextInt()
        {
            return int.Parse(next());
        }
        public int[] ArrayInt(int N, int add = 0)
        {
            int[] Array = new int[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextInt() + add;
            }
            return Array;
        }

        public long nextLong()
        {
            return long.Parse(next());
        }

        public long[] ArrayLong(int N, long add = 0)
        {
            long[] Array = new long[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextLong() + add;
            }
            return Array;
        }

        public double nextDouble()
        {
            return double.Parse(next());
        }


        public double[] ArrayDouble(int N, double add = 0)
        {
            double[] Array = new double[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextDouble() + add;
            }
            return Array;
        }
    }
}

Measured memory_bytes: 63756