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