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