/* -*- coding: utf-8 -*-
 *
 * 3710.cc:  No.3710 Universal Tiles - yukicoder
 */

#include<cstdio>
#include<bitset>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 8;
const int MAX_M = 10;
const int INF = 1 << 30;

/* typedef */

using btst = bitset<MAX_M>;
using mat = btst[MAX_M];

/* global variables */

mat ss[MAX_N][4];
int ps[MAX_N];

/* subroutines */

void rotmat(const int m, const mat a, mat b) {
  for (int i = 0; i < m; i++)
    for (int j = 0; j < m; j++)
      b[m - 1 - j][i] = a[i][j];
}

void ormat(const int m, const mat a, mat b) {
  for (int i = 0; i < m; i++) b[i] |= a[i];
}

/* main */

int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++) {
      char s[MAX_M + 4];
      scanf("%s", s);
      for (int k = 0; k < m; k++)
	ss[i][0][j][k] = (s[k] == '#');
    }

  for (int i = 0; i < n; i++)
    for (int d = 1; d < 4; d++)
      rotmat(m, ss[i][d - 1], ss[i][d]);

  int minsum = INF;
  for (;;) {
    mat t;
    for (int i = 0; i < n; i++)
      ormat(m, ss[i][ps[i]], t);

    int sum = 0;
    for (int j = 0; j < m; j++) sum += t[j].count();
    minsum = min(minsum, sum);

    int k = 0;
    while (k < n) {
      if (++ps[k] > 3) ps[k++] = 0;
      else break;
    }
    if (k >= n) break;
  }

  printf("%d\n", minsum);
  
  return 0;
}