#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, a, matrica[101][101], pas = 0;
  cin >> n;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++) {
      cin >> a;
      matrica[i][j] = a;
    }
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++) {
      if (i == j || i == ((n + 1) / 2) - 1 && j != ((n + 1) / 2) - 1 ||
          j == ((n + 1) / 2) - 1 && i != ((n + 1) / 2) - 1 ||
          i == n - j - 1 && j != ((n + 1) / 2) - 1)
        pas += matrica[i][j];
    }
  cout << pas << endl;
  return 0;
}
