using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using SB = System.Text.StringBuilder;
//using System.Threading.Tasks;
//using System.Text.RegularExpressions;
//using System.Globalization;
//using System.Diagnostics;
using static System.Console;
using System.Numerics;
using static System.Math;
using pair = Pair<int, int>;

class Program
{
    static void Main()
    {
        SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
        new Program().solve();
        Out.Flush();
    }
    readonly Scanner cin = new Scanner();
    readonly int[] dd = { 0, 1, 0, -1, 0 }; //→↓←↑
    readonly int mod = 1000000007;
    readonly int dom = 998244353;
    bool chmax<T>(ref T a, T b) where T : IComparable<T> { if (a.CompareTo(b) < 0) { a = b; return true; } return false; }
    bool chmin<T>(ref T a, T b) where T : IComparable<T> { if (b.CompareTo(a) < 0) { a = b; return true; } return false; }

    void solve()
    {
        int H = cin.nextint;
        int W = cin.nextint;

        var L = new List<int>();
        for (int i = 0; i < H; i++)
        {
            var A  = ReadLine();
            for (int j = 0; j < W; j++)
            {
                if (A[j] == '#')
                {
                    L.Add(i * W + j);
                }
            }
        }
        int[] dist;
        var far = new TwoD_BFS().BFS(H, W, L[0], out dist, L);

        WriteLine(dist[far]);

    }

}

class TwoD_BFS
{
    readonly int[] dy = { 0, 1, 0, -1 }; //→↓←↑
    readonly int[] dx = { 1, 0, -1, 0 };

    int H, W;
    int idx(int y, int x) => y * W + x;
    bool ok(int y, int x) => 0 <= y && y < H && 0 <= x && x < W;

    public int BFS(int h, int w, int s, out int[] dist, IEnumerable<int> multi = null)
    {
        H = h; W = w;
        dist = new int[H * W];
        for (int i = 0; i < dist.Length; i++) dist[i] = -1;

        var Q = new Queue<int>();
        if (multi == null) { Q.Enqueue(s); dist[s] = 0; }
        else foreach (var v in multi) { Q.Enqueue(v); dist[v] = 0; }
        int id = s;

        while (Q.Count > 0)
        {
            var u = Q.Dequeue();
            int ty = u / W;
            int tx = u % W;
            int before = dist[u];
            for (int r = 0; r < dx.Length; r++)
            {
                int y = ty + dy[r];
                int x = tx + dx[r];
                int now = idx(y, x);

                if (!ok(y, x) || dist[now] >= 0) continue;

                dist[now] = before + 1;
                id = now;
                Q.Enqueue(now);               
            }
        }
        return id;
    }
}

static class Ex
{
    public static void join<T>(this IEnumerable<T> values, string sep = " ") => WriteLine(string.Join(sep, values));
    public static string concat<T>(this IEnumerable<T> values) => string.Concat(values);
    public static string reverse(this string s) { var t = s.ToCharArray(); Array.Reverse(t); return t.concat(); }

    public static int lower_bound<T>(this IList<T> arr, T val) where T : IComparable<T>
    {
        int low = 0, high = arr.Count;
        int mid;
        while (low < high)
        {
            mid = ((high - low) >> 1) + low;
            if (arr[mid].CompareTo(val) < 0) low = mid + 1;
            else high = mid;
        }
        return low;
    }
    public static int upper_bound<T>(this IList<T> arr, T val) where T : IComparable<T>
    {
        int low = 0, high = arr.Count;
        int mid;
        while (low < high)
        {
            mid = ((high - low) >> 1) + low;
            if (arr[mid].CompareTo(val) <= 0) low = mid + 1;
            else high = mid;
        }
        return low;
    }
}

class Pair<T, U> : IComparable<Pair<T, U>> where T : IComparable<T> where U : IComparable<U>
{
    public T f; public U s;
    public Pair(T f, U s) { this.f = f; this.s = s; }
    public int CompareTo(Pair<T, U> a) => f.CompareTo(a.f) != 0 ? f.CompareTo(a.f) : s.CompareTo(a.s);
    public override string ToString() => $"{f} {s}";
}

class Scanner
{
    string[] s; int i;
    readonly char[] cs = new char[] { ' ' };
    public Scanner() { s = new string[0]; i = 0; }
    public string[] scan => ReadLine().Split();
    public int[] scanint => Array.ConvertAll(scan, int.Parse);
    public long[] scanlong => Array.ConvertAll(scan, long.Parse);
    public double[] scandouble => Array.ConvertAll(scan, double.Parse);
    public string next
    {
        get
        {
            if (i < s.Length) return s[i++];
            string st = ReadLine();
            while (st == "") st = ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            i = 0;
            return next;
        }
    }
    public int nextint => int.Parse(next);
    public long nextlong => long.Parse(next);
    public double nextdouble => double.Parse(next);
}


Measured memory_bytes: 32480