#include <iostream>
#include <vector>

using namespace std;

int main() {
    int n;
    cin >> n;
    if(n<1||n>100) {
        cout << "-1" << endl;
        return -1;
    }

    vector<vector<int>> mat(n, vector<int>(n));
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < n; j++) {
            cin >> mat[i][j];
        }
    }

    int prod = 0;

    for(int i = 0; i < n; i++) {
        prod += mat[i][i]*mat[i][n-1];
    }

    cout << prod << endl;
}