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# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using BitArray = System.Collections.BitArray;
using BigInteger = System.Numerics.BigInteger;
using TextReader = System.IO.TextReader;
using System.Text;

namespace AtCoderProject
{
    public class Program
    {
        public object Calc()
        {
            var H = consoleReader.Int;
            var W = consoleReader.Int;
            var blocks = new bool[W, H];
            var sumi = new bool[W, H];
            var count = 1;
            var current = new List<Point> { new Point() };
            var goal = new Point { h = H - 1, w = W - 1 };
            var all = 0;
            for (int h = 0; h < H; h++)
            {
                var line = consoleReader.String;
                for (int w = 0; w < W; w++)
                {
                    if (line[w] == '.')
                    {
                        blocks[w, h] = true;
                        all++;
                    }
                }
            }

            while (true)
            {
                ++count;
                var next = new List<Point>();
                foreach (var c in current)
                {
                    if (c.w > 0 && blocks[c.w - 1, c.h] && !sumi[c.w - 1, c.h])
                    {
                        sumi[c.w - 1, c.h] = true;
                        next.Add(new Point(c.w - 1, c.h));
                    }
                    if (c.w < W - 1 && blocks[c.w + 1, c.h] && !sumi[c.w + 1, c.h])
                    {
                        sumi[c.w + 1, c.h] = true;
                        next.Add(new Point(c.w + 1, c.h));
                    }
                    if (c.h > 0 && blocks[c.w, c.h - 1] && !sumi[c.w, c.h - 1])
                    {
                        var p = new Point(c.w, c.h - 1);
                        if (p.Equals(goal))
                            return all - count;
                        sumi[c.w, c.h - 1] = true;
                        next.Add(p);
                    }
                    if (c.h < H - 1 && blocks[c.w, c.h + 1] && !sumi[c.w, c.h + 1])
                    {
                        var p = new Point(c.w, c.h + 1);
                        if (p.Equals(goal))
                            return all - count;
                        sumi[c.w, c.h + 1] = true;
                        next.Add(p);
                    }
                }
                if (next.Count == 0)
                    return -1;
                current = next;
            }
        }

        struct Point : IEquatable<Point>
        {
            public int w;
            public int h;
            public Point(int x, int y)
            {
                this.w = x;
                this.h = y;
            }
            public bool Equals(Point other) => this.w == other.w && this.h == other.h;
            public override bool Equals(object obj)
            {
                if (obj is Point) return Equals((Point)obj);
                return false;
            }
            public override int GetHashCode() => w << 16 | h;
            public override string ToString() => $"({w}, {h})";
        }

        #region いつもの
#pragma warning disable
        private ConsoleReader consoleReader;
        public Program(ConsoleReader consoleReader) { this.consoleReader = consoleReader; }
        static void Main() => Console.WriteLine(new Program(new ConsoleReader(Console.In)).Calc()); static string AllLines<T>(IEnumerable<T> source) => string.Join("\n", source);
    }
    public class ConsoleReader
    {
        private string[] ReadLineSplit() => textReader.ReadLine().Split(Array.Empty<char>(), StringSplitOptions.RemoveEmptyEntries);
        private string[] line = Array.Empty<string>();
        private int linePosition;
        private TextReader textReader;
        public ConsoleReader(TextReader tr) { textReader = tr; }
        public int Int => int.Parse(String);
        public long Long => long.Parse(String);
        public double Double => double.Parse(String);
        public string String
        {
            get
            {
                if (linePosition >= line.Length)
                {
                    linePosition = 0;
                    line = ReadLineSplit();
                }
                return line[linePosition++];
            }
        }
        public class SplitLine
        {
            private string[] splited;
            public SplitLine(ConsoleReader cr) { splited = cr.ReadLineSplit(); cr.line = Array.Empty<string>(); }
            public int[] Int => String.Select(x => int.Parse(x)).ToArray();
            public int[] Int0 => String.Select(x => int.Parse(x) - 1).ToArray();
            public long[] Long => String.Select(x => long.Parse(x)).ToArray();
            public double[] Double => String.Select(x => double.Parse(x)).ToArray();
            public string[] String => splited;
        }
        public SplitLine Split => new SplitLine(this);
        public class RepeatReader : IEnumerable<ConsoleReader>
        {
            ConsoleReader cr; int count;
            public RepeatReader(ConsoleReader cr, int count) { this.cr = cr; this.count = count; }
            public IEnumerator<ConsoleReader> GetEnumerator() => Enumerable.Repeat(cr, count).GetEnumerator();
            System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() => GetEnumerator();

            public IEnumerable<string> String => this.Select(cr => cr.String);
            public IEnumerable<int> Int => this.Select(cr => cr.Int);
            public IEnumerable<int> Int0 => this.Select(cr => cr.Int - 1);
            public IEnumerable<long> Long => this.Select(cr => cr.Long);
            public IEnumerable<double> Double => this.Select(cr => cr.Double);
        }
        public RepeatReader Repeat(int count) => new RepeatReader(this, count);
    }
    #endregion
}