#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 55;
int n, m, dp[MAX_N][MAX_N][MAX_N][MAX_N];
char a[MAX_N][MAX_N];
int dfs(int x1, int y1, int x2, int y2) {
  if (dp[x1][y1][x2][y2] >= 0) {
    return dp[x1][y1][x2][y2];
  }
  if (x1 == x2 && y1 == y2) {
    return dp[x1][y1][x2][y2] = a[x1][y1] == '#';
  }
  int &ans = dp[x1][y1][x2][y2];
  ans = max(x2 - x1 + 1, y2 - y1 + 1);
  for (int i = x1; i < x2; ++i) {
    ans = min(ans, dfs(x1, y1, i, y2) + dfs(i + 1, y1, x2, y2));
  }
  for (int j = y1; j < y2; ++j) {
    ans = min(ans, dfs(x1, y1, x2, j) + dfs(x1, j + 1, x2, y2));
  }
  return ans;
}
int main() {
  scanf("%d", &n);
  memset(dp, -1, sizeof dp);
  for (int i = 1; i <= n; ++i) {
    scanf("%s", a[i] + 1);
  }
  printf("%d\n", dfs(1, 1, n, n));
}
