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.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace C_test_For_Atcorder
{

    public static class Extensions
    {
        public static string Reverse(this string sourse){
            char[] chrAry = sourse.ToCharArray();
            Array.Reverse(chrAry);
            return new string(chrAry);
        }
    }

    public class Program
    {
        public static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));
        }


        public void Solve(ConsoleInput cin)
        {
            var ans = bfs(cin);
            Console.WriteLine(ans);
            return;
        }

        const int INF = -1;
		private int bfs(ConsoleInput cin)
		{
			var H = cin.ReadInt;
			var W = cin.ReadInt;
			var sy = 0;
			var sx = 0;
			var gy = H-1;
			var gx = W-1;
			var maze = new char[H,W];
			var d = new int[H, W];//各点までの最短距離の行列

            int countS = 0;

			for (int i = 0; i < H; i++)
			{
				var str = cin.Read;
                for (int j = 0; j < W; j++)
                {
                    maze[i, j] = str[j];
                    d[i, j] = INF;//初期化
                    //初期#の数を数える
                    if (str[j] == '#') countS++;
                }
			}
			var dy = new int[] { 0, 1, 0, -1 };
			var dx = new int[] { 1, 0, -1, 0 };

			//bfs
			var que = new Queue();
			que.Enqueue(new Tuple<int, int>(sy, sx));
			d[sy, sx] = 0;//初期地点設定

			while (que.Count > 0)
			{
				Tuple<int, int> p = que.Dequeue() as Tuple<int, int>;
				if (p.Item1 == gy && p.Item2 == gx) break;
				//移動四方向をループ
				for (int i = 0; i < 4; i++)
				{
					int ny = p.Item1 + dy[i];
					int nx = p.Item2 + dx[i];

					//移動判定
					if (0 <= ny && ny < H && 0 <= nx && nx < W && maze[ny, nx] != '#' && d[ny, nx] == INF)
					{
						que.Enqueue(new Tuple<int, int>(ny, nx));
						d[ny, nx] = d[p.Item1, p.Item2] + 1;
					}
				}
			}

            if(d[gy,gx]!=INF){
                return H * W - countS - d[gy, gx]-1;
            }
			return d[gy, gx];
		}

	}

    public class ConsoleInput
    {
        private readonly System.IO.TextReader _stream;
        private char _separator = ' ';
        private Queue inputStream;

        public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
        {
            this._separator = separator;
            this._stream = stream;
            inputStream = new Queue();
        }
        public string Read
        {
            get
            {
                if (inputStream.Count != 0) return (string)inputStream.Dequeue();
                string[] tmp = _stream.ReadLine().Split(_separator);
                for (int i = 0; i < tmp.Length; ++i)
                    inputStream.Enqueue(tmp[i]);
                return (string)inputStream.Dequeue();
            }
        }
        public string ReadLine { get { return _stream.ReadLine(); } }
        public int ReadInt { get { return int.Parse(Read); } }
        public long ReadLong { get { return long.Parse(Read); } }
        public double ReadDouble { get { return double.Parse(Read); } }
        public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
        public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
        public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
    }

}