#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  int sum = 0;
  cin >> n;
  int **p;
  p = new int *[n];
  for (int i = 0; i < n; i++) {
    p[i] = new int[n];
    for (int j = 0; j < n; j++) {
      cin >> p[i][j];
    }
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (i == j || i + j == n - 1 || i == (n - 1) / 2 || j == (n - 1) / 2) {
        sum += p[i][j];
      }
    }
  }
  cout << sum;
  return 0;
}
