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++14 (GCC 5.4.1) (judge verdict: Time Limit Exceeded)

#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define ALL(A) A.begin(), A.end()

using namespace std;

typedef long long ll;
typedef pair<int, int> P;
typedef pair<P,int> PI;

const int dr[4] = {-1, 0, 1, 0};
const int dc[4] = { 0, 1, 0,-1};

char grid[52][52];
int dist[52][52];

bool bfs(int srow, int scol, int erow, int ecol){
	queue<PI> que;
	que.push(PI(P(srow, scol), 0));
	while(!que.empty()){
		PI curr = que.front(); que.pop();
		int crow = curr.first.first;
		int ccol = curr.first.second;
		int cdist = curr.second;
		dist[crow][ccol] = cdist;
		if (crow == erow && ccol == ecol){
			return true;
		} // end if

		rep (k, 4){
			int nrow = crow + dr[k];
			int ncol = ccol + dc[k];
			if (grid[nrow][ncol] == '#') continue;
			if (dist[nrow][ncol] == -1 || dist[nrow][ncol] >= cdist + 1){
				que.push(PI(P(nrow, ncol), cdist + 1));
			} // end if
		} // end rep	
	} // end while
	return false;
}

void dispGrid(int H, int W){
	for (int i = 1; i <= H; ++i){
		for (int j = 1; j <= W; ++j){
			cerr << grid[i][j];
		} // end for
		cerr << endl;
	} // end for
}

void dispDist(int H, int W){
	for (int i = 1; i <= H; ++i){
		for (int j = 1; j <= W; ++j){
			cerr << setw(2) << dist[i][j];
		} // end for
		cerr << endl;
	} // end for
}

void reversePath(int erow, int ecol){
	int crow = erow;
	int ccol = ecol;
	while(crow != 1 || ccol != 1){
		grid[crow][ccol] = ' ';
		rep (k, 4){
			int nrow = crow + dr[k];
			int ncol = ccol + dc[k];
			if (dist[nrow][ncol] + 1 == dist[crow][ccol]){
				crow = nrow;
				ccol = ncol;
				break;
			} // end if
		} // end rep
	} // end while
	grid[1][1] = ' ';
}

int countPaintBlack(int H, int W){
	int res = 0;
	for (int i = 1; i <= H; ++i){
		for (int j = 1; j <= W; ++j){
			if (grid[i][j] == '.') ++res;
		} // end for
	} // end for
	return res;
}

int main()
{
	memset(grid, 0, sizeof(grid));
	memset(dist, -1, sizeof(dist));
	rep (i, 52) rep (j, 52) grid[i][j] = '#';
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int H, W; cin >> H >> W;
	for (int i = 1; i <= H; ++i){
		for (int j = 1; j <= W; ++j){
			cin >> grid[i][j];
		} // end for
	} // end for

	int srow = 1, scol = 1;
	int erow = H, ecol = W;
	bool ans = bfs(srow, scol, erow, ecol);
	int res = -1;
	if (ans == true){
		reversePath(erow, ecol);
		res = countPaintBlack(H, W);
	} // end if

//	dispGrid(H, W);
//	dispDist(H, W);

	cout << res << endl;

	return 0;
}