#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>
using namespace std;
#define rep(i, x, limit) for (long long i = (long long)x; i < (long long)limit; i++)
#define REP(i, x, limit) for (long long i = (long long)x; i <= (long long)limit; i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define el '\n'
#define spa " "
#define Yes cout << "Yes" << el
#define No cout << "No" << el
#define YES cout << "YES" << el
#define NO cout << "NO" << el
#define inp(x) for(auto &i:x)cin>>i
#define eps (1e-10)
#define Equals(a,b) (fabs((a) - (b)) < eps )
#define debug(x) cerr << #x << " = " << x << el
using ll = long long;
using ull = unsigned long long;
using i128 = __int128_t;
using boost::multiprecision::cpp_int;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using vi = vector<int>;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using vs = vector<string>;
using vb = vector<bool>;
const double pi = 3.141592653589793238;
const int inf = 1073741823;
const ll infl = 1LL << 60;
const string ABC = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const string abc = "abcdefghijklmnopqrstuvwxyz";
const ll MOD = 998244353;
#include<atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using vm = vector<mint>;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int n,m;cin>>n>>m;
  vector<vs> S(n,vs(m));
  rep(i,0,n)rep(j,0,m){
    string s;cin>>s;
    S[i][j]=s;
  }
  vector<vector<vb>> SB(n,vector<vb>(m,vb(m)));
  rep(i,0,n)rep(j,0,m)rep(k,0,m){
    SB[i][j][k]=(S[i][j][k]=='#');
  }
  auto R=[&](auto&&f,vector<vb> X,int c)->vector<vb>{
    if(c==0)return X;
    vector<vb> stc(m,vb(m));
    rep(i,0,m)rep(j,0,m){
      stc[i][j]=X[j][m-1-i];
    }
    return f(f,stc,c-1);
  };
  auto G=[&](vector<vb> X,vector<vb> Y){
    auto Z=X;
    rep(i,0,m)rep(j,0,m){
      Z[i][j]=Z[i][j]|Y[i][j];
    }
    return Z;
  };
  auto So=[&](auto&&f,vector<vb> X,int c){
    if(c==n){
      int cnt=0;
      rep(i,0,m)rep(j,0,m)cnt+=X[i][j];
      return cnt;
    }
    int stc=m*m;
    rep(i,0,4){
      stc=min(stc,f(f,G(X,R(R,SB[c],i)),c+1));
    }
    return stc;
  };
  vector<vb> B(m,vb(m,false));
  cout<<So(So,B,0)<<el;
}