#include <iostream>
#ifdef MBP
#include "stdc++.h"
#else
#include <bits/stdc++.h>
#endif

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define REP(i, n) for (long long int i = 0, i##_len = (n); i < i##_len; ++i)
#define REP_R(i, n) for (long long int i = (n - 1); i >= 0; --i)
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((long long int)(x).size())
#define BIT(n) (1LL << (n))
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());

#define DEBUG

#ifdef DEBUG
#define OUT(x) std::cout << (x) << std::endl
#define OUT2(x, y) std::cout << (x) << "," << (y) << std::endl
#define OUT3(x, y, z) std::cout << (x) << "," << (y) << "," << (z) << std::endl
#define OUTPA(p) OUT2(p.first, p.second)
#else
#define OUT(x) NULL
#define OUT2(x, y) NULL
#define OUT3(x, y, z) NULL
#define OUTPA(p) NULL
#endif

#define INF INT_MAX
#define INFLL LLONG_MAX
#define PB push_back
#define MOD 1000000007LL

#define LSB(x) __builtin_ctzll(x)
#define MSB(x) 64LL - __builtin_clzll(x) - 1LL
#define MSBINT(x) 32LL - __builtin_clz(x)
#define BITCNT(x) __builtin_popcountll(x)

using namespace std;
using uif = uint_fast64_t;
using ll = long long int;
using vec = vector<ll>;
using mat = vector<vector<ll>>;
using pa = pair<ll, ll>;
using tTree = __gnu_pbds::tree<ll, __gnu_pbds::null_type, less<ll>, __gnu_pbds::rb_tree_tag, __gnu_pbds::tree_order_statistics_node_update>;

template <class T>
inline void input(T &arr)
{
  ll n = arr.size();
  REP(i, n)
  cin >> arr[i];
}
template <class T>
inline void inputPA(T &arr)
{
  ll n = arr.size();
  REP(i, n)
  cin >> arr[i].first >> arr[i].second;
}

template <class T>
using PQ = priority_queue<T>;
template <class T>
using PQG = priority_queue<T, vector<T>, greater<T>>;

const ll dx[4] = {1, 0, -1, 0};
const ll dy[4] = {0, 1, 0, -1};
const ll dx8[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dy8[8] = {0, 1, 1, 1, 0, -1, -1, -1};

template <class T>
bool chmax(T &, const T &);
template <class T>
bool chmin(T &, const T &);

ll qp(ll a, ll b);
ll qp(ll a, ll b, ll mo);

ll mod_pow(ll, ll);
ll mod_add(ll, ll);
ll mod_mul(ll, ll);
ll mod_div(ll, ll);
void make_fact(ll);
void make_invfact(ll);
void init_fact();

ll combination(ll, ll);

#define FACSIZE 200002LL

ll invfac[FACSIZE];
ll fac[FACSIZE];

struct edge
{
  ll to, cost, id;
};

class Graph
{
public:
  ll N;
  vector<vector<edge>> G;

  Graph(ll N) : N(N)
  {
    G = vector<vector<edge>>(N, vector<edge>(0));
  }

  void add_Directed_edge(ll from, ll to, ll cost = 1, ll id = 0)
  {
    G[from].push_back(edge({to, cost, id}));
  }

  void add_Undirected_edge(ll v1, ll v2, ll cost = 1, ll id = 0)
  {
    add_Directed_edge(v1, v2, cost, id);
    add_Directed_edge(v2, v1, cost, id);
  }

  mat waeshall_floyd()
  {
    mat d(N, vec(N, INF));
    REP(i, N)
    d[i][i] = 0;
    REP(i, N)
    for (edge e : G[i])
    {
      d[i][e.to] = min(d[i][e.to], e.cost);
    }
    REP(k, N)
    REP(i, N)
    REP(j, N)
    d[i][j] = min(d[i][j], d[i][k] + d[k][j]);

    return d;
  }
  vec dikstra(ll x)
  {
    vec distance(N, INF);
    distance[x] = 0;
    PQG<pa> pque;
    pque.push(make_pair(0, x));

    while (!pque.empty())
    {

      auto pq = pque.top();
      pque.pop();
      for (auto e : G[pq.second])
      {
        ll d = distance[pq.second] + e.cost;
        if (d < distance[e.to])
        {
          distance[e.to] = d;
          pque.push(make_pair(d, e.to));
        }
      }
    }

    return distance;
  }
};

bool check(ll i, ll j, ll h, ll w)
{
  //if (c == '#')
  //    return false;
  if (i < 0 || j < 0)
    return false;
  if (i >= h || j >= w)
    return false;
  return true;
}
ll enc(ll i, ll j, ll w)
{
  return i * w + j;
}
pa dec(ll x, ll w)
{
  return make_pair(x / w, x % w);
}

int main(void)
{
  ll h, w;
  cin >> h >> w;
  vector<vector<char>> B(h, vector<char>(w));
  REP(i, h)
  {
    input(B[i]);
  }
  auto G = Graph(h * w);
  ll white = 0;
  ll black = 0;
  REP(i, h)
  {
    REP(j, w)
    {
      if (B[i][j] == '#')
      {
        black++;
        continue;
      }
      white++;
      REP(k, 4)
      {
        ll y = i + dy[k];
        ll x = j + dx[k];
        if (check(y, x, h, w))
        {
          if (B[y][x] != '#')
          {
            G.add_Directed_edge(enc(i, j, w), enc(y, x, w), 1, 0);
          }
        }
      }
    }
  }
  //auto ma = G.waeshall_floyd();
  auto ve = G.dikstra(enc(0, 0, w));
  //auto val = ma[enc(0, 0, w)][enc(h - 1, w - 1, w)];
  auto val = ve[enc(h - 1, w - 1, w)];
  //OUT(val);
  if (val > 1000000)
  {
    cout << -1 << endl;
    return 0;
  }
  cout << white - val - 1 << endl;

  return 0;
}

template <class T>
bool chmax(T &a, const T &b)
{
  if (a < b)
  {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool chmin(T &a, const T &b)
{
  if (b < a)
  {
    a = b;
    return 1;
  }
  return 0;
}

ll qp(ll a, ll b)
{
  ll ans = 1LL;
  do
  {
    if (b & 1LL)
      ans = 1LL * mod_mul(ans, a) % MOD;
    a = 1LL * mod_mul(a, a) % MOD;
  } while (b >>= 1LL);
  return ans;
}
ll qp(ll a, ll b, ll mo)
{
  ll ans = 1LL;
  do
  {
    if (b & 1LL)
      ans = 1LL * (ans % mo) * (a % mo);
    a = 1LL * (a % mo) * (a % mo);
  } while (b >>= 1LL);
  return ans;
}

ll mod_pow(ll x, ll r)
{
  if (r == 0)
    return 1;
  else if (r == 1)
    return x % MOD;
  else if (r % 2 == 0)
  {
    ll t = mod_pow(x, r / 2) % MOD;
    return t * t % MOD;
  }
  else
  {
    ll t = mod_pow(x, r / 2) % MOD;
    ll k = t * t % MOD;
    return k * x % MOD;
  }
}
ll mod_add(ll a, ll b)
{
  return (a + b) % MOD;
}

ll mod_mul(ll a, ll b)
{
  return (a * b) % MOD;
}

ll mod_div(ll a, ll b)
{
  return mod_mul(a, mod_pow(b, MOD - 2));
}

void make_fact(ll n)
{
  fac[0] = 1;
  REP(i, n)
  {
    fac[i + 1] = mod_mul(fac[i], i + 1);
  }
}

void make_invfact(ll n)
{
  invfac[n] = mod_pow(fac[n], MOD - 2);
  REP_R(i, n)
  {
    invfac[i] = mod_mul(invfac[i + 1], i + 1);
  }
}

void init_fact()
{
  make_fact(FACSIZE - 1);
  make_invfact(FACSIZE - 1);
}

ll combination(ll n, ll c)
{

  return mod_mul(fac[n], mod_mul(invfac[c], invfac[n - c]));
}
///////////////fact
/*
  init_fact();
  cout << fac[5] << endl;
  cout << invfac[5] << endl;
  cout << combination(8, 4) << endl;
  cout << combination(31, 8) << endl;
  //*/
///////////////////

Measured memory_bytes: 640