#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  static char s[8][12][12];
  rep(z, n) rep(i, m) cin >> s[z][i];
  static int d[12][12];
  int ans = m * m;
  auto dfs = [&](auto&& self, int z) -> void {
    if (z == n) {
      int cnt = 0;
      rep(i, m) rep(j, m) cnt += d[i][j] != 0;
      chmin(ans, cnt);
      return;
    }
    rep(_, 4) {
      rep(i, m) rep(j, m) d[i][j] += s[z][i][j] == '#';
      self(self, z + 1);
      rep(i, m) rep(j, m) d[i][j] -= s[z][i][j] == '#';
      if (z == 0) return;
      static char t[12][12];
      rep(i, m) rep(j, m) t[i][j] = s[z][m-1-j][i];
      rep(i, m) rep(j, m) s[z][i][j] = t[i][j];
    }
  };
  dfs(dfs, 0);
  cout << ans << '\n';
}