#include <bits/stdc++.h>

using namespace std;
const int N = 10;
int a[N][N];

int main() {
    int n = 3;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            cin >> a[i][j];

    int s = 0;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            if (i == j) s += a[i][j];

    cout << s << endl;
    return 0;
}