#include <bits/stdc++.h>

using namespace std;
using ll = long long;

int main()
{
    ll n;
    cin >> n;
    vector<vector<ll>> z1(n, vector<ll>(n, 0));
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            cin >> z1.at(i).at(j);
        }
    }
    ll pr, sN = 0, sS = 0, sE = 0, sW = 0;
    if (n % 2 == 0)
    {
        pr = n / 2 - 1;
    }
    else
    {
        pr = n / 2;
    }

    for (int i = 0, h = 1; i < pr; i++, h++)
    {
        int w;
        sN += accumulate(z1.at(i).begin() + h, z1.at(i).begin() + n - h, w);
    }
    cout << sN << endl;

    return 0;
}