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# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace AtCoder.D
{
    public class Program
    {
        public static long H { get; private set; }
        public static long W { get; private set; }

        public static void Main() { var r = GetResult(); Debug.WriteLine(r); Console.Write(r); }

        private static object GetResult()
        {
            (H, W) = Read2Longs();
            var table_isBlack = new bool[H, W];
            var blackCount = 0L;
            for (int i = 0; i < H; i++)
            {
                var l = ReadText();
                for (int j = 0; j < W; j++)
                {
                    var isBlack = l[j] == '#';
                    table_isBlack[i, j] = isBlack;
                    if (isBlack) blackCount++;
                }
            }

            // 最短経路を求めて、通らなかった白マスを黒にぬればよい
            var step = CreateStepTable();
            step[0, 0] = 0;
            var queue = new Queue<Point>();
            queue.Enqueue(new Point(0, 0));
            while (queue.Count > 0)
            {
                var p = queue.Dequeue();

                var nextPonints = new Point[]
                {
                    new Point(p.H + 1, p.W),
                    new Point(p.H - 1, p.W),
                    new Point(p.H, p.W + 1),
                    new Point(p.H, p.W - 1),
                };

                foreach (var next in nextPonints)
                {
                    if (next.H < 0 || next.H == H) continue;
                    if (next.W < 0 || next.W == W) continue;
                    if (table_isBlack[p.H, p.W]) continue;
                    // 到達済みの場合
                    if (step[next.H, next.W] != -1) continue;

                    queue.Enqueue(next);
                    step[next.H, next.W] = step[p.H, p.W] + 1;
                }
            }

            var shortestStep = step[H - 1, W - 1];
            if (shortestStep == -1) return -1;

            return H * W - blackCount - (shortestStep + 1);
        }

        private static long[,] CreateStepTable()
        {
            var t = new long[H, W];
            for (int i = 0; i < H; i++)
            {
                for (int j = 0; j < W; j++)
                {
                    t[i, j] = -1;
                }
            }

            return t;
        }

        class Point
        {
            public int H { get; set; }
            public int W { get; set; }

            public Point(int h, int w)
            {
                H = h;
                W = w;
            }
        }

        #region Console.Read

        public static string ReadText() { return Console.ReadLine(); }
        public static List<string> ReadTexts() { return Console.ReadLine().Split(' ').ToList(); }
        public static long ReadLong() { return long.Parse(Console.ReadLine()); }
        public static (long, long) Read2Longs() { var ls = ReadLongs(); return (ls[0], ls[1]); }
        public static (long, long, long) Read3Longs() { var ls = ReadLongs(); return (ls[0], ls[1], ls[2]); }
        public static (long, long, long, long) Read4Longs() { var ls = ReadLongs(); return (ls[0], ls[1], ls[2], ls[3]); }
        public static (long, long, long, long, long) Read5Longs() { var ls = ReadLongs(); return (ls[0], ls[1], ls[2], ls[3], ls[4]); }
        public static List<long> ReadLongs() { return Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToList(); }

        #endregion
    }
}