#include <bits/stdc++.h>
#include <atcoder/all>
//#pragma GCC optimize("O2")
using namespace std;
using namespace atcoder;
using ll = long long;
using ull = unsigned long long;
using vi = vector<int>;
using vll = vector<ll>;
using vull = vector<ull>;
using vs = vector<string>;
using vb = vector<bool>;
using vc = vector<char>;
using vf = vector<float>;
using vd = vector<double>;
using vvi = vector<vector<int>>;
using vvll = vector<vector<ll>>;
using vvull = vector<vector<ull>>;
using vvs = vector<vector<string>>;
using vvc = vector<vector<char>>;
using vvb = vector<vector<bool>>;
using vvf = vector<vector<float>>;
using vvd = vector<vector<double>>;
using pi = pair<int, int>;
using pll = pair<ll, ll>;
using vpi = vector<pi>;
using vpll = vector<pll>;
#define cYes cout << "YES\n"
#define cNo cout << "NO\n"
#define cyes cout << "Yes\n"
#define cno cout << "No\n"
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
template <typename T>
inline istream& operator >> (istream& is, vector<T>& v){
    for(size_t i=0; i<v.size(); i++){
        is >> v[i];
    }
    return is;
}
template <typename T, typename U>
inline istream& operator >> (istream& is, vector<pair<T,U>>& v){
    for(size_t i=0; i<v.size(); i++){
        is >> v[i].first >> v[i].second;
    }
    return is;
}
template <typename T>
inline istream& operator >> (istream& is, vector<vector<T>>& v){
    for(size_t i=0; i<v.size(); i++){
        for(size_t j=0; j<v[i].size(); j++){
            is >> v[i][j];
        }
    }
    return is;
}
template <typename T, typename U, typename S, typename V>
inline istream& operator >> (istream& is, vector<pair<pair<T,U>, pair<S,V>>>& v){
    for(size_t i=0; i<v.size(); i++){
        is >> v[i].first.first >> v[i].first.second >> v[i].second.first >> v[i].second.second;
    }
    return is;
}
const double PI = 3.14159265359;
vi dx = {0, -1, 0, 1};
vi dy = {1, 0, -1, 0};

void rot90(vvc &G, ll &M){
    vvc NG(M, vc(M));
    for(int i=0; i<M; i++){
        for(int j=0; j<M; j++){
            NG[M-1-j][i] = G[i][j];
        }
    }
    G = NG;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    ll N, M;
    cin >> N >> M;
    vector<vvc> S(N, vvc(M, vc(M)));
    for(int i=0; i<N; i++){
        cin >> S[i];
    }
    ll J = 1;
    for(int i=0; i<N; i++){
        J *= 4;
    }
    ll ans = INT_MAX;
    for(int b=0; b<=J; b++){
        ll bi = 1;
        vvi G(M, vi(M, 0));
        for(int i=0; i<N; i++){
            for(int j=0; j<(b/bi%4); j++){
                rot90(S[i], M);
            }
            for(int y=0; y<M; y++){
                for(int x=0; x<M; x++){
                    if(S[i][y][x] == '#') G[y][x]++;
                }
            }
            for(int j=0; j<(4-(b/bi%4))%4; j++){
                rot90(S[i], M);
            }
            // cout << (b/bi%4) << " ";
            bi *= 4;
        }
        ll cnt = 0;
        for(int i=0; i<M; i++){
            for(int j=0; j<M; j++){
                if(G[i][j] >= 1) cnt++;
            }
        }
        // cout << cnt << "\n";
        ans = min(ans, cnt);
    }
    cout << ans << "\n";
}