#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n, a, i, j, mid, cnt = 0;
  cin >> n;
  for (i = 0; i < n; i++) {
    for (j = 0; j < n; j++) {
      cin >> a;
      if (i == j) cnt = cnt + a;
      if (i + j == n - 1) cnt = cnt + a;
      if (i == n / 2) cnt = cnt + a;
      if (j == n / 2) cnt = cnt + a;
      if (i == n / 2 && j == n / 2) mid = a;
    }
  }
  cout << cnt - (3 * mid) << endl;
  return 0;
}
