second

#include <iostream>

using namespace std;

int main()
{
    int N, a[100][100], sum = 0;
    cin >> N;
    for (int i = 0; i < N; i++) {
        for (int k = 0; k < N; k++) {
            cin >> a[i][k];
            if (i%2== 0) sum+=a[i][k];
        }
    }
    cout << sum;
    return 0;
}