#include <bits/stdc++.h>
#ifdef LOCAL
#include <debug.hpp>
#else
#define debug(...) void(0)
#endif

struct BipartiteMatching {
    int U, V, t;
    bool solved;
    std::vector<std::vector<int>> G;
    std::vector<int> L, R, visited;

    BipartiteMatching(int U, int V) : U(U), V(V), t(0), solved(false), G(U), L(U, -1), R(V, -1), visited(U, -1) {}

    void add_edge(int u, int v) {
        assert(0 <= u && u < U);
        assert(0 <= v && v < V);
        G[u].emplace_back(v);
    }

    void shuffle() {
        static std::mt19937 mt;
        for (auto& v : G) std::shuffle(v.begin(), v.end(), mt);
    }

    int solve() {
        for (bool updated = true; std::exchange(updated, false); t++) {
            for (int i = 0; i < U; i++) {
                if (L[i] == -1) {
                    updated |= dfs(i);
                }
            }
        }
        solved = true;
        return U - std::count(L.begin(), L.end(), -1);
    }

    std::vector<std::pair<int, int>> max_matching() const {
        assert(solved);
        std::vector<std::pair<int, int>> res;
        for (int i = 0; i < U; i++) {
            if (~L[i]) {
                res.emplace_back(i, L[i]);
            }
        }
        return res;
    }

private:
    bool dfs(int u) {
        if (std::exchange(visited[u], t) == t) return false;
        for (int& v : G[u]) {
            if (R[v] == -1) {
                L[u] = v, R[v] = u;
                return true;
            }
        }
        for (int& v : G[u]) {
            if (dfs(R[v])) {
                L[u] = v, R[v] = u;
                return true;
            }
        }
        return false;
    }
};

using namespace std;

typedef long long ll;
#define all(x) begin(x), end(x)
constexpr int INF = (1 << 30) - 1;
constexpr long long IINF = (1LL << 60) - 1;
constexpr int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};

template <class T> istream& operator>>(istream& is, vector<T>& v) {
    for (auto& x : v) is >> x;
    return is;
}

template <class T> ostream& operator<<(ostream& os, const vector<T>& v) {
    auto sep = "";
    for (const auto& x : v) os << exchange(sep, " ") << x;
    return os;
}

template <class T, class U = T> bool chmin(T& x, U&& y) { return y < x and (x = forward<U>(y), true); }

template <class T, class U = T> bool chmax(T& x, U&& y) { return x < y and (x = forward<U>(y), true); }

template <class T> void mkuni(vector<T>& v) {
    sort(begin(v), end(v));
    v.erase(unique(begin(v), end(v)), end(v));
}

template <class T> int lwb(const vector<T>& v, const T& x) { return lower_bound(begin(v), end(v), x) - begin(v); }

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N, M;
    cin >> N >> M;
    vector<string> S(N);
    cin >> S;

    vector idx(N, vector<int>(M));
    vector<int> cnt(2, 0);
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < M; j++) {
            if (S[i][j] == '#') continue;
            int x = (i ^ j) & 1;
            idx[i][j] = cnt[x]++;
        }
    }
    int original;
    {
        BipartiteMatching BM(cnt[0], cnt[1]);
        for (int i = 0; i < N; i++) {
            for (int j = 0; j < M; j++) {
                if ((i ^ j) & 1) continue;
                if (S[i][j] == '#') continue;
                for (int d = 0; d < 4; d++) {
                    int ni = i + dx[d], nj = j + dy[d];
                    if (clamp(ni, 0, N - 1) != ni or clamp(nj, 0, M - 1) != nj) continue;
                    if (S[ni][nj] == '#') continue;
                    BM.add_edge(idx[i][j], idx[ni][nj]);
                }
            }
        }
        original = BM.solve();
    }
    auto calc = [&](int x, int y) {
        BipartiteMatching BM(cnt[0], cnt[1]);
        for (int i = 0; i < N; i++) {
            for (int j = 0; j < M; j++) {
                if ((i ^ j) & 1) continue;
                if (S[i][j] == '#') continue;
                if (i == x and j == y) continue;
                for (int d = 0; d < 4; d++) {
                    int ni = i + dx[d], nj = j + dy[d];
                    if (clamp(ni, 0, N - 1) != ni or clamp(nj, 0, M - 1) != nj) continue;
                    if (S[ni][nj] == '#') continue;
                    if (ni == x and nj == y) continue;
                    BM.add_edge(idx[i][j], idx[ni][nj]);
                }
            }
        }
        return BM.solve();
    };
    int ans = 0;
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < M; j++) {
            if (S[i][j] == '#') continue;
            ans += (calc(i, j) == original);
        }
    }

    cout << ans << '\n';
    return 0;
}