#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> bool mmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T> bool mmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; }
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;

vector<string> S;

struct GridGraph
{

    int H, W;
    std::vector<int> dx = {1, -1, 0, 0};
    std::vector<int> dy = {0, 0, 1, -1};

    GridGraph() = default;
    GridGraph(int h, int w) : H(h), W(w) {}

    /* Implement here. */
    using T_E = long long int;
    const T_E INF = 1e18;
    inline T_E edge_cost(int x_s, int y_s, int x_t, int y_t)
    {
        if (S[x_s][y_s] == '#') return 1e9;
        if (S[x_t][y_t] == '#') return 1e9;
        return 1;
    }

    // Dijkstra's algorithm
    // Complexity: O(HWlog(HW))
    std::vector<std::vector<T_E>> dij; // Distance from (x_s, y_s)
    std::vector<std::vector<std::pair<int, int>>> dij_prv; // Previous node for Dijkstra optimal path
    void dijkstra(int x_s, int y_s) {
        dij.assign(H, std::vector<T_E>(W, INF));
        dij_prv.assign(H, std::vector<std::pair<int, int>>(W, std::make_pair(-1, -1)));

        using P = std::tuple<T_E, int, int>;
        std::priority_queue<P, std::vector<P>, std::greater<P>> pq;
        pq.emplace(0, x_s, y_s);
        while (!pq.empty()) {
            T_E dnow;
            int x, y;
            std::tie(dnow, x, y) = pq.top();
            pq.pop();
            if (dij[x][y] < dnow) continue;
            for (size_t d = 0; d < dx.size(); d++) {
                int xn = x + dx[d], yn = y + dy[d];
                if (xn < 0 or yn < 0 or xn >= H or yn >= W) continue;
                T_E dnxt = dnow + edge_cost(x, y, xn, yn);
                if (dnxt < dij[xn][yn]) {
                    dij[xn][yn] = dnxt;
                    dij_prv[xn][yn] = std::make_pair(x, y);
                    pq.emplace(dnxt, xn, yn);
                }
            }
        }
    }
};
int main()
{
    int H, W;
    cin >> H >> W;
    S.resize(H);
    cin >> S;
    GridGraph g(H, W);
    g.dijkstra(0, 0);
    int ret = 0;
    for (auto s : S) for (auto c : s) ret += (c == '.');
    if (g.dij.back().back() >= 1e9) puts("-1");
    else cout << ret - g.dij.back().back() - 1 << endl;
}



Measured memory_bytes: 384