#include <bits/stdc++.h>
#define rep(i,n) for (int i = (0); i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define limit(x,l,r) max(l,min(x,r))
#define lims(x,l,r) (x = max(l,min(x,r)))
#define isin(x,l,r) ((l) <= (x) && (x) < (r))
#define show(x) cout << #x << " = " << (x) << endl
#define show2(x,y) cout << #x << " = " << (x) << ", " << #y << " = " << (y) << endl
#define show3(x,y,z) cout << #x << " = " << (x) << ", " << #y << " = " << (y) <<  ", " << #z << " = " << (z) << endl
#define showv(v) rep(i,v.size()) printf("%d%c", v[i], i==v.size()-1?'\n':' ')
#define showv2(v) rep(j,v.size()) showv(v[j])
#define showt(t,n) rep(i,n) printf("%d%c", t[i], i==n-1?'\n':' ')
#define showt2(t,r,c) rep(j,r) showt(t[j],c)
#define showvp(p) rep(i,p.size()) printf("%d %d\n", p[i].first, p[i].second);
#define printv(v) rep(i,v.size()) printf("%d\n", v[i])
#define printt(t,n) rep(i,n) printf("%d\n", t[i])
#define incl(v,x) find(rng(v),x)!=v.end()
#define incls(s,c) s.find(c)!=string::npos
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcountll
#define bit(n,k) ((n>>k)&1) // nのk bit目
#define bn(x) ((1<<x)-1)
#define dup(x,y) (((x)+(y)-1)/(y))
#define newline puts("")
#define uni(x) x.erase(unique(rng(x)),x.end())
#define SP << " " <<
#define v(T) vector<T>
#define vv(T) v(v(T))
using namespace std;
using ll = long long;
using ld = long double;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vs = vector<string>;
using P = pair<int, int>;
using T = tuple<int, int, int>;
using vp = vector<P>;
using vt = vector<T>;
const int mod = 1000000007;
const double EPS = 1e-9;
//const long double EPS = 1e-14;
const int INF = (1<<30)-1;
const ll LINF = (1LL<<62)-1;
#define dame { puts("No"); return 0;}
#define yn {puts("Yes");}else{puts("No");}
inline int in() { int x; scanf("%d",&x); return x;}
inline ll lin() { ll x; scanf("%lld",&x); return x;}
inline char chin() { char x; scanf("%c",&x); return x;}
inline string stin() { string x; cin >> x; return x;}
inline double din() { double x; scanf("%lf",&x); return x;}
//template<class T = int> inline T in() { T x; cin >> x; return (x);}
template<typename T>inline ll suma(const v(T)& a) { ll res(0); for (auto&& x : a) res += x; return res;}
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
char itoa(int n) { return n + '0';}
ll gcd(ll a, ll b) { return b ? gcd(b,a%b) : a;}
ll lcm(ll a, ll b) { return a/gcd(a,b)*b;}
const int dx[4] = {1, 0,-1, 0};
const int dy[4] = {0, 1, 0,-1};

int main () {
  int h, w;
  cin >> h >> w;
  vector<string> s(h);
  rep(i,h) cin >> s[i];

  auto bfs = [&](int sy, int sx, int gy, int gx) {
    vvi d(h,vi(w,INF));
    d[sy][sx] = 1;
    //vv(P) prev(h,v(P)(w,P(-1,-1)));
    //int sy = 0, sx = 0, gy = h-1, gx = w-1;
    queue<P> q;
    q.push(P(sy,sx));
    while(!q.empty()) {
      P p = q.front(); q.pop();
      int y = p.fi, x = p.se;
      if (y == gy && x == gx) break;
      rep(i,4) {
        int ny = y + dy[i];
        int nx = x + dx[i];
        if (!(isin(ny,0,h) && isin(nx,0,w))) continue;
        if (s[ny][nx] == '#') continue;
        if (d[ny][nx] != INF) continue;
        d[ny][nx] = d[y][x] + 1;
        //prev[ny][nx] = P(y,x);
        q.push(P(ny,nx));
      }
    }
    return d[gy][gx];
  };

  int x = bfs(0,0,h-1,w-1);
  int cnt = 0;
  rep(i,h)rep(j,w) {
    if (s[i][j] == '.') cnt++;
  }
  if (x == INF) cout << -1 << endl;
  else cout << cnt - x << endl;
  return 0;
}

Measured memory_bytes: 256