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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define QUEUE_SIZE 10000000	//待ち行列の大きさ

int queue[QUEUE_SIZE];
int front;	//待ち行列の先頭
int rear;	//待ち行列の末尾

#define next(a) (((a)+1)%QUEUE_SIZE)

/*待ち行列を初期化する*/
void init(){
	front = rear = 0;
}
/*待ち行列にデータを入れる*/
void enqueue(int x){
	if(next(rear)==front){
		printf("待ち行列がフルなので要素を入れられません");
		exit(1);
	}
	queue[rear] = x;
	rear = next(rear);
}
/*待ち行列からデータを取り出す*/
int dequeue(){
	int x;
	if(front==rear){
		printf("待ち行列が空なので要素を取り出せません");
		exit(1);
	}
	x = queue[front];
	front = next(front);
	return x;
}
/*待ち行列が空かどうかを調べる*/
/*空なら1、空で無ければ0を返す*/
int empty(){
	return front == rear;
}

int main(void){
	init();
	int dx[4]={-1,0,0,1};
	int dy[4]={0,-1,1,0};
	int i,j;
	int h,w;
	int white = 0;
	scanf("%d%d",&h,&w);
	char s[h][w+1];
	int v[h][w];
	for(i=0;i<h;i++){
		scanf("%s",s[i]);
	}
	for(i=0;i<h;i++)for(j=0;j<w;j++){
		v[i][j]=-1;
		if(s[i][j]=='.')white++;
	}
	int temp,x,y;
	enqueue(0);
	v[0][0]=0;
	while(empty()==0){
		temp = dequeue();
		x = temp/1000;
		y = temp%1000;
		for(i=0;i<4;i++){
			if( (x+dx[i]<0)||(x+dx[i]>=h)||(y+dy[i]<0)||(y+dy[i])>=w)continue;
			if(s[x+dx[i]][y+dy[i]]=='.'&&v[x+dx[i]][y+dy[i]]==-1){
				v[x+dx[i]][y+dy[i]] = v[x][y]+1;
				enqueue((x+dx[i])*1000+y+dy[i]);
			}
		}
	}
	printf("%d",white - v[h-1][w-1]-1);
	return 0;
}