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>
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define rep(i, s, N) for (ll i{s}; i < (N); i++)
#define rem(i, N, s) for (ll i{N}; i > (s); i--)
#define debug(x) cerr << #x << ": " << x << '\n'
#define debugp(i) cerr << "(" << i.first << ", " << i.second << ")\n"
#define debugv(v) cerr << #v << ": ";for(auto&& i : v) cerr << i << " "; cerr << '\n'
#define debugvp(v) cerr << #v << ": ";for(auto&& i : v) cerr << "(" << i.first << ", " << i.second << ") "; cerr << '\n'
const int MOD = (int)1e9 + 7;
const long double pi = 3.141592653589793238462643383279L;
using namespace std;
using ll = long long;
using ld = long double;
using str = string;
using wstr = wstring;
const string rt = "\n", sp = " ";
const wstring wrt = L"\n", wsp = L" ";

/* GCD */
template <typename M, typename N>
constexpr common_type_t<M, N> gcd(M a, N b) { return b != 0 ? gcd(b, a % b) : a; }

/* LCM */
template <typename M, typename N>
constexpr common_type_t<M, N> lcm(M a, N b) { return a * b / gcd(a, b); }

/* UNIONFIND */
template <typename T>
struct UnionFind
{
  vector<T> par;
  UnionFind(T n) : par(n, -1) {}
  void init(T n) { par.assign(n, -1); }
  T root(T x)
  {
    if (par[x] < 0)
      return x;
    else
      return par[x] = root(par[x]);
  }
  bool issame(T x, T y) { return root(x) == root(y); }
  bool merge(T x, T y)
  {
    x = root(x);
    y = root(y);
    if (x == y)
      return false;
    if (par[x] > par[y])
      swap(x, y);
    par[x] += par[y];
    par[y] = x;
    return true;
  }
  int size(int x) { return -par[root(x)]; }
};

/* COMB */
auto comb(ll N){
  vector<vector<ll>> v(N+1,vector<ll>(N+1));
  for(unsigned int i = 0;i <v.size(); i++){
    v[i][0]=1;
    v[i][i]=1;
  }
  for(unsigned int k = 1;k <v.size();k++){
    for(unsigned int j = 1;j<k;j++){
      v[k][j]=(v[k-1][j-1]+v[k-1][j]);
    }
  }
  return v;
}
auto comb(ll N, ll n){
  vector<vector<ll>> v(max(N+1,n+1),vector<ll>(max(N+1,n+1)));
  for(unsigned int i = 0;i <v.size(); i++){
    v[i][0]=1;
    v[i][i]=1;
  }
  for(unsigned int k = 1;k <v.size();k++){
    for(unsigned int j = 1;j<k;j++){
      v[k][j]=(v[k-1][j-1]+v[k-1][j]);
    }
  }
  return v[N][n];
}

/* COMB % MOD */
template <typename T>
ll combpm(T N_, T C_)
{
  const int NUM_ = 400001;
  static ll fact[NUM_ + 1], factr[NUM_ + 1], inv[NUM_ + 1];
  if (fact[0] == 0)
  {
    inv[1] = fact[0] = factr[0] = 1;
    for (int i = 2; i <= NUM_; ++i)
      inv[i] = inv[MOD % i] * (MOD - MOD / i) % MOD;
    for (int i = 1; i <= NUM_; ++i)
      fact[i] = fact[i - 1] * i % MOD, factr[i] = factr[i - 1] * inv[i] % MOD;
  }
  if (C_ < 0 || C_ > N_)
    return 0;
  return factr[C_] * fact[N_] % MOD * factr[N_ - C_] % MOD;
}

/* MAKE VECTOR */
template <class T>
constexpr vector<T> make_vector(size_t a) { return vector<T>(a); }
template <class T, class... Ts>
auto make_vector(size_t a, Ts... ts) { return vector<decltype(make_vector<T>(ts...))>(a, make_vector<T>(ts...)); }

/* MAKE DEQUE */
template <class T>
constexpr deque<T> make_deque(size_t a) { return deque<T>(a); }
template <class T, class... Ts>
auto make_deque(size_t a, Ts... ts) { return deque<decltype(make_deque<T>(ts...))>(a, make_deque<T>(ts...)); }

/* TEST */
void test(ll n) { cout << "test" << n << endl; }

/* PRECISION */
void fixsp(ll n) { cout << fixed << setprecision(n); }
void defsp(ll n) { cout << defaultfloat << setprecision(n); }

/* WEIGHTENED UNIONFIND */
struct WUnionFind
{
  vector<int> par;
  vector<int> rank;
  WUnionFind(int n = 1) { init(n); }
  void init(int n = 1)
  {
    par.resize(n);
    rank.resize(n);
    for (int i = 0; i < n; ++i)
      par[i] = i, rank[i] = 0;
  }
  int root(int x)
  {
    if (par[x] == x)
    {
      return x;
    }
    else
    {
      int r = root(par[x]);
      return par[x] = r;
    }
  }
  bool issame(int x, int y) { return root(x) == root(y); }
  bool merge(int x, int y)
  {
    x = root(x);
    y = root(y);
    if (x == y)
      return false;
    if (rank[x] < rank[y])
      swap(x, y);
    if (rank[x] == rank[y])
      ++rank[x];
    par[y] = x;
    return true;
  }
};

/* DIVISOR */
deque<ll> divisor(ll n)
{
  deque<ll> ret;
  for (ll i = 1; i * i <= n; i++)
  {
    if (n % i == 0)
    {
      ret.push_back(i);
      if (i * i != n)
        ret.push_back(n / i);
    }
  }
  sort(begin(ret), end(ret));
  return (ret);
}

/* MODE */
template <typename T>
auto mode(T data)
{
  if (data.size() == 1)
    return *begin(data);
  sort(begin(data), end(data));
  typename decltype(data)::value_type mode{};
  size_t n{}, count{1};
  for (auto iter = adjacent_find(begin(data), end(data)), last = end(data), next = end(data); iter != last;)
  {
    next = upper_bound(iter, last, *iter);
    count = distance(iter, next);
    if (n < count)
      n = count, mode = *iter;
    iter = adjacent_find(next, last);
  }
  return mode;
}

/* MEDIAN */
template <typename T>
auto median(T data)
{
  sort(begin(data), end(data));
  size_t median_index = data.size() / 2;
  return (data.size() % 2 == 0 ? static_cast<double>(data[median_index] + data[median_index - 1]) / 2 : data[median_index]);
}

/* INT POW */
template <typename T>
T multi(T a, ll b)
{
  T ans{1};
  for (int i{}; i < b; i++)
    ans *= a;
  return ans;
}

/* INF */
template <typename T>
constexpr T inf() { return numeric_limits<T>::max(); } 

/* FASTER IO */
void fastio(ll a)
{
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  cerr.tie(nullptr);
  if(a) fixsp(a);
}

/* MIN COST FLOW */
template <typename flow_t, typename cost_t>
struct PrimalDual
{
  const cost_t INF;
  struct edge
  {
    int to;
    flow_t cap;
    cost_t cost;
    int rev;
    bool isrev;
  };
  vector<vector<edge>> graph;
  vector<cost_t> potential, min_cost;
  vector<int> prevv, preve;
  PrimalDual(int V) : graph(V), INF(numeric_limits<cost_t>::max()) {}
  void add_edge(int from, int to, flow_t cap, cost_t cost)
  {
    graph[from].emplace_back((edge){to, cap, cost, (int)graph[to].size(), false});
    graph[to].emplace_back((edge){from, 0, -cost, (int)graph[from].size() - 1, true});
  }
  cost_t min_cost_flow(int s, int t, flow_t f)
  {
    int V = (int)graph.size();
    cost_t ret = 0;
    using Pi = pair<cost_t, int>;
    priority_queue<Pi, vector<Pi>, greater<Pi>> que;
    potential.assign(V, 0);
    preve.assign(V, -1);
    prevv.assign(V, -1);
    while (f > 0)
    {
      min_cost.assign(V, INF);
      que.emplace(0, s);
      min_cost[s] = 0;
      while (!que.empty())
      {
        Pi p = que.top();
        que.pop();
        if (min_cost[p.second] < p.first)
          continue;
        for (int i = 0; i < graph[p.second].size(); i++)
        {
          edge &e = graph[p.second][i];
          cost_t nextCost = min_cost[p.second] + e.cost + potential[p.second] - potential[e.to];
          if (e.cap > 0 && min_cost[e.to] > nextCost)
          {
            min_cost[e.to] = nextCost;
            prevv[e.to] = p.second, preve[e.to] = i;
            que.emplace(min_cost[e.to], e.to);
          }
        }
      }
      if (min_cost[t] == INF)
        return -1;
      for (int v = 0; v < V; v++)
        potential[v] += min_cost[v];
      flow_t addflow = f;
      for (int v = t; v != s; v = prevv[v])
      {
        addflow = min(addflow, graph[prevv[v]][preve[v]].cap);
      }
      f -= addflow;
      ret += addflow * potential[t];
      for (int v = t; v != s; v = prevv[v])
      {
        edge &e = graph[prevv[v]][preve[v]];
        e.cap -= addflow;
        graph[v][e.rev].cap += addflow;
      }
    }
    return ret;
  }
  void output()
  {
    for (int i = 0; i < graph.size(); i++)
    {
      for (auto &e : graph[i])
      {
        if (e.isrev)
          continue;
        auto &rev_e = graph[e.to][e.rev];
        cout << i << "->" << e.to << " (flow: " << rev_e.cap << "/" << rev_e.cap + e.cap << ")" << endl;
      }
    }
  }
};

/* BELLMANFORD */

vector<long long> BellmanFord(int s, int V, vector<tuple<long long,long long,long long>> &G)
{
  vector<long long> d(V, inf<long long>());
  vector<bool> neg(V);
  d[s] = 0;
  for (int i = 0; i < V - 1; ++i)
  {
    for (auto &&e : G)
    {
      if (d[get<0>(e)] == inf<long long>())
        continue;
      d[get<1>(e)] = min(d[get<1>(e)], d[get<0>(e)] + get<2>(e));
    }
  }
  for (int i = 0; i < V; ++i)
  {
    for (auto &&e : G)
    {
      if (d[get<0>(e)] == inf<long long>())
        continue;
      if (d[get<1>(e)] > d[get<0>(e)] + get<2>(e))
      {
        d[get<1>(e)] = d[get<0>(e)] + get<2>(e);
        neg[get<1>(e)] = 1;
      }
      if (neg[get<0>(e)])
        neg[get<1>(e)] = 1;
    }
  }
  for (int i = 0; i < V; i++)
  {
    if (neg[i])
      d[i] = -inf<long long>();
  }
  return d;
}

/* DIJKSTRA */

vector<long long> Dijkstra(int s, int V, vector<tuple<long long,long long,long long>> &G){
  vector<vector<pair<long long,long long>>> uv(V);
  for(auto&& i : G) uv[get<0>(i)].emplace_back(get<1>(i), get<2>(i));
  vector<long long> d(V, inf<long long>()/2);
  vector<long long> prev(V, -1);
  d[s] = 0;
  priority_queue<pair<long long,long long>,vector<pair<long long,long long>>,greater<pair<long long,long long>>> Q;
  rep(i,0,V) Q.emplace(d[i], i);
  while(!Q.empty()){
    long long u = Q.top().second;
    Q.pop();
    for(auto&& v : uv[u]){
      long long alt = d[u] + v.second;
      if(d[v.first] > alt){
        d[v.first] = alt;
        if(d[v.first] > inf<long long>()/4) d[v.first] = inf<long long>()/2;
        else if(d[v.first] < -inf<long long>()/4) d[v.first] = -inf<long long>()/2;
        prev[v.first] = u;
        Q.emplace(alt, v.first);
      }
    }
  }
  for(auto&& i : d){
    if(abs(i)>inf<long long>()/4) (i*=2)++;
  }
  return d;
}

/* BFS */

vector<long long> BFS(long long s, long long V, vector<pair<long long,long long>> &G){
  queue<long long> Q;
  vector<vector<long long>> uv(V);
  for(auto&& i : G) uv[i.first].emplace_back(i.second);
  vector<long long> d(V,inf<long long>());
  d[s] = 0;
  Q.emplace(s);
  while(!Q.empty()){
    long long v = Q.front();
    Q.pop();
    for(auto&& i : uv[v]){
      if(d[i] == inf<long long>()){
        d[i] = d[v]+1;
        Q.emplace(i);
      }
    }
  }
  return d;
}

/* WARSHALLFLOYD */
vector<vector<long long>> WarshallFloyd(int V, vector<tuple<long long,long long,long long>> &G){
  vector<vector<long long>> d(V, vector<long long>(V, inf<long long>()));
  for(auto&& i : G){
    d[get<0>(i)][get<1>(i)] = get<2>(i);
  }
  rep(k,0,V) rep(i,0,V) rep(j,0,V){
    if(d[i][k] != inf<ll>() && d[k][j] != inf<ll>())
    d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
  }
  rep(i,0,V){
    d[i][i] = 0;
  }
  return d;
}

/* NUITA.INC & KYOTO UNIVERSITY */

/* LAST EDITED ON 9.5.2019 */

/* CODE STARTS FROM HERE */

int main(){
  fastio(0);
  ll H, W;
  cin >> H >> W;
  auto G = make_deque<char>(H,W);
  ll rem{};
  rep(i,0,H) rep(j,0,W){
    cin >> G[i][j];
    if(G[i][j] == '.') rem++;
  }
  queue<tuple<ll,ll,ll>> Q;
  Q.emplace(0,0,0);
  while(!Q.empty()){
    pair<ll,ll> now = {get<0>(Q.front()),get<1>(Q.front())};
    ll dist = get<2>(Q.front());
    Q.pop();
    if(now.first < 0 || H <= now.first) continue;
    if(now.second < 0 || W <= now.second) continue;
    if(G[now.first][now.second] == '#') continue;
    G[now.first][now.second] = '#';
    if(now == make_pair(H-1,W-1)){
      cout << rem - 1 - dist << rt;
      return 0;
    }
    Q.emplace(now.first+1,now.second,dist+1);
    Q.emplace(now.first-1,now.second,dist+1);
    Q.emplace(now.first,now.second+1,dist+1);
    Q.emplace(now.first,now.second-1,dist+1);
  }
  cout << -1 << rt;
}