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 Java8 (OpenJDK 1.8.0) (judge verdict: Time Limit Exceeded)

import java.util.*;
import java.io.IOException;
import java.io.InputStream;

class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
    public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();}

    public String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while(isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }

    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    }

    public double nextDouble() { return Double.parseDouble(next());}
}

public class Main {

    static class Edge {
        int from, to;

        public Edge(int from, int to) {
            this.from = from;
            this.to = to;
        }
    }

    static class Pair {
        int h, w;

        public Pair(int h, int w) {
            this.h = h;
            this.w = w;
        }
    }

    static void bfs() {
        visited = new boolean[H][W];
        visited[0][0] = true;
        prev = new Pair[H][W];
        prev[0][0] = new Pair(-1, -1);

        Deque<Pair> que = new ArrayDeque<>();
        que.offer(new Pair(0, 0));

        while (!que.isEmpty()) {
            Pair pair = que.poll();
            int ch = pair.h;
            int cw = pair.w;
            visited[ch][cw] = true;
            if (ch == H-1 && cw == W-1) break;
            for (int dir = 0; dir < 4; ++dir) {
                int nh = ch + dy[dir];
                int nw = cw + dx[dir];

                if (nh < 0 || nh >= H || nw < 0 || nw >= W) continue;
                if (grid[nh][nw] == '#') continue;
                if (visited[nh][nw]) continue;

                prev[nh][nw] = pair;
                que.offer(new Pair(nh, nw));
            }
        }
    }

    static int H;
    static int W;
    static int res = 1;
    static List<List<Edge>> graph;
    static boolean[][] visited;
    static char[][] grid;
    static Pair[][] prev;
    static int[] dx = {-1, 1, 0, 0};
    static int[] dy = {0, 0, -1, 1};

    public static void main(String[] args) {
        FastScanner fs = new FastScanner();
        H = fs.nextInt();
        W = fs.nextInt();
        grid = new char[H][W];
        for (int i = 0; i < H; ++i) grid[i] = fs.next().toCharArray();
        int black = 0;
        for (int i = 0; i < H; ++i) {
            for (int j = 0; j < W; ++j) {
                if (grid[i][j] == '#') ++black;
            }
        }

        bfs();

        if (visited[H-1][W-1]) {
            int h = H - 1;
            int w = W - 1;
            while (true) {
                Pair pair = prev[h][w];
                if (pair.h == -1 && pair.w == -1) break;
                else ++res;
                h = pair.h;
                w = pair.w;
            }
//            System.out.println(res);
            System.out.println((H * W - black - res));
        }
        else
            System.out.println(-1);
    }
}