#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, sum = 0;
  cin >> n;
  int m[n][n];
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) cin >> m[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 += m[i][j];
    }
  }
  cout << sum;
  return 0;
}
