#include <bits/stdc++.h>

using namespace std;

int dx[4]{0, 0, 1, -1};
int dy[4]{1, -1, 0, 0};

int main() {
    cin.tie(0)->sync_with_stdio(false);
    int n, m;
    cin >> n >> m;
    vector<vector<char>> a(n, vector<char>(m, 0));
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            cin >> a[i][j];
        }
    }
    auto match = [&] {
        vector<vector<int>> g(n * m);
        vector<int> match(n * m, -1);
        for (int i = 0; i < n; ++i) {
            for (int j = 0; j < m; ++j) {
                if (a[i][j] == '#')continue;
                for (int k = 0; k < 4; ++k) {
                    int new_i = i + dx[k], new_j = j + dy[k];
                    if (new_i >= 0 && new_i < n && new_j >= 0 && new_j < m && a[new_i][new_j] == '.') {
                        g[i * m + j].push_back(new_i * m + new_j);
                    }
                }
            }
        }
        vector<int> used(n * m, -1);
        int timer = 0;
        auto dfs = [&](int v, auto &&dfs) -> bool {
            if (used[v] == timer)return false;
            used[v] = timer;
            for (auto to: g[v]) {
                if (match[to] == -1) {
                    match[to] = v;
                    return true;
                }
            }
            for (auto to: g[v]) {
                if (dfs(match[to], dfs)) {
                    match[to] = v;
                    return true;
                }
            }
            return false;
        };
        for (int v = 0; v < n * m; ++v) {
            if (dfs(v, dfs))++timer;
        }
        return timer;
    };
    int res = n * m;
    int exp = match();
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            if (a[i][j] == '#'){
                --res;
                continue;
            }
            a[i][j] = '#';
            res -= match() != exp;
            a[i][j] = '.';
        }
    }
    cout << res;
}