#include <bits/stdc++.h>
using namespace std;
const int M = 2010;
int A[M][M];
int col[M];
int diag[M];
int main() {
  ios_base::sync_with_stdio(false);
  int i, j, k, n;
  char str[M];
  scanf("%d", &n);
  for (i = 0; i < n; i++) {
    scanf("%s", str);
    for (j = 0; j < n; j++) A[i][j] = str[j] - '0';
  }
  int sum = 0;
  for (i = n - 1; i > 0; i--) {
    int inv = 0;
    for (j = 0; j < i; j++) {
      if (A[i][j] != (inv ^ col[j])) {
        inv ^= 1;
        sum++;
        diag[i] ^= 1;
        diag[j] ^= 1;
        col[j] ^= 1;
      }
    }
  }
  memset((col), (0), sizeof(col));
  for (i = 0; i < n - 1; i++) {
    int inv = 0;
    for (j = n - 1; j > i; j--) {
      if (A[i][j] != (inv ^ col[j])) {
        inv ^= 1;
        sum++;
        diag[i] ^= 1;
        diag[j] ^= 1;
        col[j] ^= 1;
      }
    }
  }
  for (i = 0; i < n; i++)
    if (A[i][i] != diag[i]) sum++;
  printf("%d\n", sum);
  return 0;
}
