Problem:
Score: 400 points

Problem statement

We have an H \times W grid whose squares are painted black or white. The square at the i-th row from the top and the j-th column from the left is denoted as (i, j).

Snuke would like to play the following game on this grid. At the beginning of the game, there is a character called Kenus at square (1, 1). The player repeatedly moves Kenus up, down, left or right by one square. The game is completed when Kenus reaches square (H, W) passing only white squares.

Before Snuke starts the game, he can change the color of some of the white squares to black. However, he cannot change the color of square (1, 1) and (H, W). Also, changes of color must all be carried out before the beginning of the game.

When the game is completed, Snuke's score will be the number of times he changed the color of a square before the beginning of the game. Find the maximum possible score that Snuke can achieve, or print -1 if the game cannot be completed, that is, Kenus can never reach square (H, W) regardless of how Snuke changes the color of the squares.

The color of the squares are given to you as characters s_{i, j}. If square (i, j) is initially painted by white, s_{i, j} is .; if square (i, j) is initially painted by black, s_{i, j} is #.

Constraints

H is an integer between 2 and 50 (inclusive).

W is an integer between 2 and 50 (inclusive).

s_{i, j} is . or # (1 \leq i \leq H, 1 \leq j \leq W).

s_{1, 1} and s_{H, W} are ..

Input

Input is given from Standard Input in the following format:

H W
s_{1, 1}s_{1, 2}s_{1, 3} ... s_{1, W}
s_{2, 1}s_{2, 2}s_{2, 3} ... s_{2, W}
: :
s_{H, 1}s_{H, 2}s_{H, 3} ... s_{H, W}

Output

Print the maximum possible score that Snuke can achieve, or print -1 if the game cannot be completed.

Sample Input 1

3 3
..#
#..
...

Sample Output 1

2

The score 2 can be achieved by changing the color of squares as follows:

Sample Input 2

10 37
.....................................
...#...####...####..###...###...###..
..#.#..#...#.##....#...#.#...#.#...#.
..#.#..#...#.#.....#...#.#...#.#...#.
.#...#.#..##.#.....#...#.#.###.#.###.
.#####.####..#.....#...#..##....##...
.#...#.#...#.#.....#...#.#...#.#...#.
.#...#.#...#.##....#...#.#...#.#...#.
.#...#.####...####..###...###...###..
.....................................

Sample Output 2

209

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

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 Edge = Pair<long, int>;
using System.Text;
class Program
{ 
    static void Main(string[] args)
    {
        Solve();
        //WriteLine(Solve());
    }
    static int[] hw;
    static char[][] gred;
    static void Solve()
    {
        hw = Input.ar;
        gred = Input.gred(hw[0]);
        var wh = gred.Sum(v => v.Count(c => c == '.'));
        var d = bfs();
        WriteLine(d[hw[0]-1,hw[1]-1]==int.MaxValue?-1: wh - d[hw[0]-1, hw[1]-1] - 1);
    }

    static int[] gh = new[] { 0, 0, 1, -1 };
    static int[] gw = new[] { 1, -1, 0, 0 };
    static int[,] bfs()
    {
        var que = new Queue<Pair<int, int>>();
        var dist = new int[hw[0], hw[1]];
        for (var i = 0; i < hw[0]; i++)
            for (var j = 0; j < hw[1]; j++)
                dist[i, j] = int.MaxValue;
        que.Enqueue(new Pair<int, int>(0, 0));
        dist[0, 0] = 0;
        while (que.Any())
        {
            var p = que.Dequeue();
            for (var i = 0; i < 4; i++)
            {
                var h = p.v1 + gh[i];
                var w = p.v2 + gw[i];
                if (!Search.Inside(h, w, hw) || gred[h][w] == '#' || dist[h, w] != int.MaxValue) continue;
                dist[h, w] = dist[p.v1, p.v2] + 1;
                que.Enqueue(new Pair<int, int>(h, w));
            }
        }
        return dist;
    }
}

public class Input
{
    public static string read => ReadLine().Trim();
    public static int[] ar => read.Split(' ').Select(int.Parse).ToArray();
    public  static int num => ToInt32(read);
    public static long[] arL => read.Split(' ').Select(long.Parse).ToArray();
    public  static long numL => ToInt64(read);
    public static char[][] gred(int h) 
        => Enumerable.Repeat(0, h).Select(_ => read.ToCharArray()).ToArray();
    public static int[] ar1D(int n)
        => Enumerable.Repeat(0, n).Select(_ => num).ToArray();
    public static long[] arL1D(int n)
        => Enumerable.Repeat(0, n).Select(_ => numL).ToArray();
    public static int[][] ar2D(int n)
        => Enumerable.Repeat(0, n).Select(_ => ar).ToArray();
    public static long[][] arL2D(int n)
        => Enumerable.Repeat(0, n).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>(IList<T> array,T value)
        where T : IComparable<T>
    {
        var low = 0;
        var high = array.Count;
        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>(IList<T> array,T value)
        where T : IComparable<T>
    {
        var low = 0;
        var high = array.Count;
        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 Inside(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()}";
}