#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

void rotate(vector<string> &s) {
    int n = s.size();
    auto t = s;
    rep(i, n) rep(j, n) {
        t[i][j] = s[j][n - i - 1];
    }
    s = t;
}

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);

    int n, m;
    cin >> n >> m;
    vector<vector<string>> s(n, vector<string>(m));
    rep(i, n) rep(j, m) cin >> s[i][j];
    int ans = m * m;
    vector<vector<int>> cur(m, vector<int>(m, 0));
    function<void(int)> rec = [&](int i) {
        if (i == n) {
            int s = 0;
            rep(j, m) rep(k, m) {
                if (cur[j][k])
                    s++;
            }
            ans = min(ans, s);
            return;
        }
        rep(r, 4) {
            rep(j, m) rep(k, m) {
                if (s[i][j][k] == '#')
                    cur[j][k]++;
            }
            rec(i + 1);
            rep(j, m) rep(k, m) {
                if (s[i][j][k] == '#')
                    cur[j][k]--;
            }
            rotate(s[i]);
        }
        return;
    };
    rec(0);
    cout << ans << endl;

    return 0;
}