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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Collection;
import java.util.Scanner;
import java.util.Queue;
import java.util.ArrayDeque;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        GridRepainting solver = new GridRepainting();
        solver.solve(1, in, out);
        out.close();
    }

    static class GridRepainting {
        int[] route;

        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int h = in.nextInt();
            int w = in.nextInt();

            int[][] map = new int[h][w];

            route = new int[h * w];
            for (int i = 0; i < h; i++) {
                String s = in.next();
                char[] chars = s.toCharArray();
                for (int j = 0; j < w; j++) {
                    if (chars[j] == '.') {
                        map[i][j] = 1;
                    }
                }
            }
            int[] ret = dijkstra(0, 0, map);
            int width = map[0].length;
            int minus = 0;
            if (ret[ret.length - 1] == Integer.MAX_VALUE) {
                out.println(-1);
                return;
            }

            int[] miti = getRoute(map);
            for (int i = 0; i < h; i++) {
                for (int j = 0; j < w; j++) {
                    if (i == 0 && j == 0) {
                        continue;
                    }
                    if (i + 1 == h && j + 1 == w) {
                        continue;
                    }
                    if (map[i][j] == 1) {
                        if (miti[i * width + j] > 0) {
                            continue;
                        }
                        minus++;
                    }
                }
            }
            out.println(minus);
        }

        int[] getRoute(int[][] map) {
            int h = map.length;
            int w = map[0].length;

            int[] ret = new int[h * w];
            int pos = h * w - 1;
            while (true) {
                int next = route[pos];
                ret[next] = pos;
                if (next == 0) {
                    break;
                }
                pos = next;
            }
            return ret;
        }

        int[] dijkstra(int x, int y, int[][] map) {
            if (map[y][x] == 0) {
                return new int[0];
            }
            int h = map.length;
            int w = map[0].length;

            int[] distance = new int[h * w];
            Arrays.fill(distance, Integer.MAX_VALUE);

            distance[y * w + x] = 0;

            Queue<Pair> pq = new ArrayDeque<>();
            pq.add(new Pair(x, y));

            int[] nx = {-1, 1, 0, 0};
            int[] ny = {0, 0, -1, 1};

            while (!pq.isEmpty()) {
                Pair p = pq.poll();
                for (int i = 0; i < nx.length; i++) {
                    int xx = p.x + nx[i];
                    int yy = p.y + ny[i];
                    if (canMove(xx, yy, map)) {
                        if (distance[yy * w + xx] > distance[p.y * w + p.x] + map[yy][xx]) {
                            distance[yy * w + xx] = distance[p.y * w + p.x] + map[yy][xx];

                            route[yy * w + xx] = p.y * w + p.x;
                            pq.add(new Pair(xx, yy));
                        }
                    }
                }
            }
            return distance;
        }

        public boolean canMove(int x, int y, int[][] map) {
            return isInside(x, y, map) && map[y][x] != 0;
        }

        public boolean isInside(int x, int y, int[][] map) {
            int h = map.length;
            if (h <= 0) {
                return false;
            }
            int w = map[0].length;
            if (w <= 0) {
                return false;
            }

            if (x < 0 || y < 0) {
                return false;
            }
            return h > y && w > x;
        }

        public class Pair {
            public final Integer x;
            public final Integer y;

            public Pair(Integer x, Integer y) {
                this.x = x;
                this.y = y;
            }

        }

    }
}