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 System.Text;
using System.Threading.Tasks;

namespace ConsoleApp5 {
    class Program {
        //スタートから(x, y)までの最短距離
        static int[,] cost;

        static int H;
        static int W;

        static int[,] s;

        static void Main(string[] args) {
            var S = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
            H = S[0];
            W = S[1];
            
            cost = new int[H, W];

            //全ての白マスの数の合計
            int white = 0;
            //解答
            int ans = -1;

            //全ての要素を-1にする
            for (int i = 0; i < H; i++) {
                for (int j = 0; j < W; j++) {
                    cost[i, j] = -1;
                }
            }

            //全ての点の情報を記憶しておく
            s = new int[H, W];
            for (int i = 0; i < H; i++) {
                string X = Console.ReadLine();
                for (int j = 0; j < W; j++) {
                    s[i, j] = X[j];
                    if (X[j] == '.') {
                        white++;  //ここで白マスをカウント
                    }
                }
            }

            //最短距離
            int min_cost = bfs();

            //出力
            if (min_cost == -1) {
                ans = -1;
            } else {
                ans = white - (min_cost + 1);
            }
            Console.WriteLine(ans);
        }

        static int bfs() {
            //座標をpair(y, x)でもってqueueに入れる
            Queue<Tuple<int, int>> que = new Queue<Tuple<int, int>>();
            //スタートは(0, 0)
            Tuple<int, int> inQueue = Tuple.Create(0, 0);
            que.Enqueue(inQueue);
            cost[0, 0] = 0;

            //移動可能なマスをループで簡単に列挙
            int[] dx = { 0, 1, 0, -1 };
            int[] dy = { 1, 0, -1, 0 };

            //キューが空になるまで繰り返す
            while (que.Count != 0) {
                Tuple<int, int> p = que.Dequeue();  //キューの先端を取得しつつ削除

                //ゴールに到達したらcostを返す
                if (p.Item1 == H - 1 && p.Item2 == W - 1) {
                    return cost[p.Item1, p.Item2];
                }

                //今の地点から、上下左右に向かって調査する
                for (int i = 0; i < 4; i++) {
                    //次のx座標とy座標
                    int ny = p.Item1 + dy[i];
                    int nx = p.Item2 + dx[i];

                    //エリア外に行ったら、次のループに入る
                    if (nx < 0 || ny < 0 || nx >= W || ny >= H) continue;
                    //壁にぶち当たったら、次のループに入る
                    if (s[ny, nx] == '#') continue;
                    //すでに探索済みだったら、次のループに入る
                    if (cost[ny, nx] != -1) continue;

                    cost[ny, nx] = cost[p.Item1, p.Item2] + 1;
                    Tuple<int, int> inQ = Tuple.Create(ny, nx);
                    que.Enqueue(inQ);
                }
            }
            return -1;
        }
    }
}