#include <stdio.h>
int main(){
    int n;
    scanf("%d", &n);
    int a[100] [100];
    int sum = 0;
    for (int i = 0; i <n n; i++) {
        for (int j = 0;j < n; j++) {
        scanf("%d", &a[i][j]);
        if (i == j) {
            sum += a[i][j];
        }
       }
    }
    printf("%d",sum);
    return 0;
}