#include<stdio.h> int main() { int arr[10][10] = { 0 }; int i = 0; int j = 0; int n = 0; scanf("%d", &n); int sum = 0; for (i = 0; i < n; i++) { for (j = 0; j < n; j++) { scanf("%d", &arr[i][j]); while (i > j) { sum += arr[i][j]; break; } } } if (sum == 0) { printf("YES\n"); } else { printf("NO\n"); } return 0; }