#include <bits/stdc++.h>
using namespace std;
int n;
int main() {
  cin >> n;
  int ans = 0;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++) {
      int a;
      cin >> a;
      if (i == j || i + j == n - 1 || i == n / 2 || j == n / 2) ans += a;
    }
  cout << ans;
}
