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: Accepted)

#include <bits/stdc++.h>
using namespace std;
#define incant() cin.tie(0), ios::sync_with_stdio(false)
#define int long long
#define double long double
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define lb lower_bound
#define ub upper_bound
#define X first
#define Y second
#define gcd __gcd
template<class T> using pque = priority_queue<T>;
using vint = vector<int>;
using vstr = vector<string>;
using pint = pair<int, int>;
using vp = vector<pint>;
using mint = map<int, int>;
using dict = map<string, int>;
using sint = set<int>;
using sp = set<pint>;
using qint = queue<int>;
using qp = queue<pint>;
using pqint = pque<int>;
using pqp = pque<pint>;
#define chmax(x, y) x = max(x, y)
#define chmin(x, y) x = min(x, y)
#define sz(x) x.size()
#define all(x) (x).begin(), (x).end()
#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) repi(i, 0, n)
#define repi(i, a, b) for(int i = (int)(a); i < (int)(b); i++)
#define rep(...) _overload(__VA_ARGS__, repi, _rep,)(__VA_ARGS__)
#define _rev(i, n) revi(i, n, 0)
#define revi(i, a, b) for(int i = (int)(a - 1); i >= (int)(b); i--)
#define rev(...) _overload(__VA_ARGS__, revi, _rev,)(__VA_ARGS__)
#define each(i, n) for(auto&& i: n)
#define inv(x) each(i, x) in(i)
#define out(x) cout << (x)
#define space() cout << " "
#define indent() cout << '\n'
#define printv(x) each(i, x) out(i), space(); indent()
#define debug(x, ...) cerr << __LINE__ << ": " << #x << ": " << (x) << '\n'
#define YN(x) print((x) ? "YES" : "NO")
#define Yn(x) print((x) ? "Yes" : "No")
#define yn(x) print((x) ? "yes" : "no")
#define POS(x) print((x) ? "POSSIBLE" : "IMPOSSIBLE")
#define Pos(x) print((x) ? "Possible" : "Impossible")
#define pos(x) print((x) ? "possible" : "impossible")
void in(){}
template<typename F, typename... R> void in(F& f, R&... r){
    cin >> f, in(r...);
}
void print(){
    indent();
}
template<typename F, typename... R> void print(F& f, R&... r){
    out(f), space(), print(r...);
}
const int INF = 1e16, MOD = 1e9 + 7, LIMIT = 100001, S_LIMIT = 101;
const int dx[] = {0, 0, 1, 0, -1, -1, 1, 1, -1}, dy[] = {0, -1, 0, 1, 0, -1, -1, 1, 1};
const string alphabet = "abcdefghijklmnopqrstuvwxyz";
const string ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
int g[S_LIMIT][S_LIMIT] = {};
int lcm(int a, int b){
    return a/gcd(a, b)*b;
}
int modpw(int x, int n){
    return n < 2 ? x : modpw(x*x%MOD, n/2)*(n%2 ? x : 1)%MOD;
}
int factorial(int a){
    return a < 2 ? 1 : factorial(a - 1)*a;
}
int summation(int a){
    return a < 1 ? 0 : (a*a + a)/2;
}
int combination(int n, int r){
    int res = 1;
    rep(i, 1, r + 1){
        res *= n--, res /= i;
    }
    return res;
}
int modcomb(int n, int r){
    return factorial(n)*modpw(factorial(r), MOD - 2)%MOD*modpw(factorial(n - r), MOD - 2)%MOD;
}
bool isPrime(int n){
    rep(i, 2, sqrt(n) + 1){
        if(i > 3){
            i++;
        }
        if(!(n%i)){
            return false;
        }
    }
    return true;
}
void warshall(int n){
    rep(i, n){
        rep(j, n){
            rep(k, n){
                chmin(g[j][k], g[j][i] + g[i][k]);
            }
        }
    }
}
mint factoriazation(int n){
    mint ans;
    rep(i, 2, sqrt(n) + 1){
        if(i > 3){
            i++;
        }
        while(!(n%i)){
            ans[i]++, n /= i;
        }
    }
    if(n > 1){
        ans[n]++;
    }
    return ans;
}
struct UF{
    vint t;
    UF(int size): t(size, -1){}
    int root(int x){
        return t[x] < 0 ? x : t[x] = root(t[x]);
    }
    int size(int x){
        return -t[root(x)];
    }
    bool isSame(int x, int y){
        return root(x) == root(y);
    }
    bool unite(int x, int y){
        x = root(x), y = root(y);
        if(x != y){
            if(t[y] < t[x]){
                swap(x, y);
            }
            t[x] += t[y], t[y] = x;
        }
        return x != y;
    }
};
int a, b, c, k, n, m, x, y, w, h, res = 0, cnt = 0, sum = 0, mx = -INF, mn = INF;
string s, t;
char maze[S_LIMIT][S_LIMIT];

int search(){
    qp q;
    int dp[h][w];
    rep(i, h){
        rep(j, w){
            dp[i][j] = INF;
        }
    }
    q.push(mp(0, 0));
    dp[0][0] = 0;
    while(sz(q)){
        pint p = q.front(); q.pop();
        if(p.X == w - 1 && p.Y == h - 1){
            break;
        }
        rep(i, 1, 5){
            int nx = p.X + dx[i], ny = p.Y + dy[i];
            if(0 <= nx && nx < w && 0 <= ny && ny < h && maze[ny][nx] != '#' && dp[ny][nx] == INF){
                q.push(mp(nx, ny)), dp[ny][nx] = dp[p.Y][p.X] + 1;
            }
        }
    }
    return dp[h - 1][w - 1];
}

main(){
    incant();
    in(h, w);
    rep(i, h){
        rep(j, w){
            in(maze[i][j]);
            if(maze[i][j] == '.'){
                res++;
            }
        }
    }
    out(max(-1LL, res - search() - 1));
}