#include <bits/stdc++.h>
using namespace std;
const int dim = 52;
char a[dim][dim];
int s[dim][dim];
int dp[dim][dim][dim][dim];
void compute(int i1, int j1, int i2, int j2) {
  if (dp[i1][j1][i2][j2] != 0x3f3f3f3f) return;
  int ans = max(i2 - i1 + 1, j2 - j1 + 1);
  if (s[i2][j2] - s[i1 - 1][j2] - s[i2][j1 - 1] + s[i1 - 1][j1 - 1] == 0) {
    dp[i1][j1][i2][j2] = 0;
    return;
  }
  if (s[i2][j2] - s[i1 - 1][j2] - s[i2][j1 - 1] + s[i1 - 1][j1 - 1] ==
      (i2 - i1 + 1) * (j2 - j1 + 1)) {
    dp[i1][j1][i2][j2] = ans;
    return;
  }
  for (int i = i1; i < i2; ++i) {
    compute(i1, j1, i, j2);
    compute(i + 1, j1, i2, j2);
    ans = min(ans, dp[i1][j1][i][j2] + dp[i + 1][j1][i2][j2]);
  }
  for (int j = j1; j < j2; ++j) {
    compute(i1, j1, i2, j);
    compute(i1, j + 1, i2, j2);
    ans = min(ans, dp[i1][j1][i2][j] + dp[i1][j + 1][i2][j2]);
  }
  dp[i1][j1][i2][j2] = ans;
}
void solve() {
  int n;
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i] + 1;
    for (int j = 1; j <= n; ++j)
      s[i][j] = s[i - 1][j] + s[i][j - 1] - s[i - 1][j - 1] + (a[i][j] == '#');
  }
  memset(dp, 0x3f, sizeof dp);
  compute(1, 1, n, n);
  cout << dp[1][1][n][n];
}
int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  solve();
  return 0;
}
