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: Runtime Error)

using System;
using System.Text;
using System.Collections.Generic;
using System.Linq;
 
class Program {
    static int[,] Step;
    static long H;
    static long W;
    static string[] grid;
    static void Main(string[] args) {
        var HW  = Console.ReadLine().Split().Select(a => long.Parse(a)).ToArray();
        H = HW[0];
        W = HW[1];
        
        //マスの合計値
        var sum = H*W;
       
        //マスの情報を記録する
        grid = new string[H];
        for(int i = 0; i < H;i++){
          grid[i] = Console.ReadLine();
        }
      
        //通行不可能なマスの数を調べる
        var imp = 0; 
        for(int i = 0; i < H;i++){
          for(int j = 0; j < W;j++){
            if(grid[i][j] == '#'){
              imp++;
            }
          }
        }
        //通行可能なマスの総数
        var avl = sum-imp; 

        //幅優先探索でゴールまでの最短距離を求める
        Step = new int[H+1,W+1];
        WidthFirstSearch(1,1);
        //Console.WriteLine(Step[3,3]);
        var MinStep = Step[H,W];
        //Console.WriteLine((MinStep-1));
        if(MinStep > 0){
          Console.WriteLine(avl-(MinStep));
        }else{
          Console.WriteLine(-1);
        }
        
  }
  
  static void WidthFirstSearch(long H1,long W1){
    var queue = new MyQueue();
    if(grid[0][0] == '.'){
      queue.Enque(H1,W1);
    }
    Step[H1,W1] = 1;
    
    while (!(queue.isEmpty())){
      var top = queue.Deque();
      var tH = top.H;
      var tW = top.W;
      
      //上をキューに登録
      if(tH > 1 && Step[tH-1,tW] == 0&& grid[(int)(tH-2)][(int)(tW-1)] == '.'
        ){
        
        Step[tH-1,tW] = Step[tH,tW]+1;
        queue.Enque(tH-1,tW);
      }
      //下をキューに登録
      if(tH < H && Step[tH+1,tW] == 0 && grid[(int)(tH)][(int)(tW-1)] == '.'){
        Step[tH+1,tW] = Step[tH,tW]+1;
        queue.Enque(tH+1,tW);
      }
      //右をキューに登録
      if(tW < W && Step[tH,tW+1] == 0 && grid[(int)(tH-1)][(int)(tW)] == '.'){
        Step[tH,tW+1] = Step[tH,tW]+1;
        queue.Enque(tH,tW+1);
      }
      //左をキューに登録
      if(tW > 1 && Step[tH,tW-1] == 0 && grid[(int)(tH-2)][(int)(tW-1)] == '.'){
        Step[tH,tW-1] = Step[tH,tW]+1;
        queue.Enque(tH,tW-1);
      }
      
      
    }
  }
         
}

class MyQueue
{
    public Masu[] datas = new Masu[5000];
    public int enpoint = -1;
    public int depoint = -1;
    public void Enque(long H,long W)
    {
        this.enpoint++;
        var data = new Masu(H,W);
        datas[this.enpoint] = data;
    }
    public Masu Deque()
    {
        this.depoint++;
        return datas[this.depoint];
    }
 
    public bool isEmpty()
    {
        return (this.depoint == this.enpoint);
    }
}

class Masu
{
  public long H;
  public long W;
  public Masu(long H,long W){
    this.H = H;
    this.W = W;
  }
}