#include <bits/stdc++.h>
using namespace std;
using ll=long long;
const ll ILL=2167167167167167167;
const int INF=2100000000;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using pq_ = priority_queue<T, vector<T>, greater<T>>;
template<class T> int LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> int UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,T b){if(b<a){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,T b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
bool yneos(bool a,bool upp=false){if(a){cout<<(upp?"YES\n":"Yes\n");}else{cout<<(upp?"NO\n":"No\n");}return a;}
template<class T> void vec_out(vector<T> &p,int ty=0){
    if(ty==2){cout<<'{';for(int i=0;i<(int)p.size();i++){if(i){cout<<",";}cout<<'"'<<p[i]<<'"';}cout<<"}\n";}
    else{if(ty==1){cout<<p.size()<<"\n";}for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){T ans=T(0);for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(int)(a&1),a>>=1;}return res;}
template<class T> T square(T a){return a * a;}



void solve();
// DEAR MYSTERIES / TOMOO
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t = 1;
    // cin >> t;
    rep(i, 0, t) solve();
}

void solve(){
    int N, M;
    cin >> N >> M;
    vector S(N, vector(M, vector<int>(M)));
    rep(i, 0, N) rep(j, 0, M) rep(k, 0, M) {
        char c;
        cin >> c;
        if (c == '#') S[i][j][k] = 1;
    }
    int ans = INF;
    vector tmp(M, vector<int>(M));
    tmp = S[0];
    auto f = [&](auto self, int ind) -> void {
        if (ind == N) {
            int sum = 0;
            rep(i, 0, M) rep(j, 0, M) sum += min(1, tmp[i][j]);
            chmin(ans, sum);
            return;
        }
        rep(rp, 0, 4) {
            vector nx(M, vector<int>(M));
            rep(i, 0, M) rep(j, 0, M) nx[i][j] = S[ind][j][M - 1 - i];
            swap(nx, S[ind]);
            rep(i, 0, M) rep(j, 0, M) tmp[i][j] += S[ind][i][j];
            self(self, ind + 1);
            rep(i, 0, M) rep(j, 0, M) tmp[i][j] -= S[ind][i][j];
        }
    };
    f(f, 1);
    cout << ans << "\n";
}