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