#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, i, j, s1 = 0, s2 = 0, s3 = 0, s4 = 0;
  int a[105][105];
  cin >> n;
  int k = (n + 1) / 2;
  for (i = 1; i <= n; i++) {
    for (j = 1; j <= n; j++) {
      cin >> a[i][j];
    }
    cout << endl;
  }
  for (i = 1; i <= n; i++) {
    s1 += a[i][k];
  }
  for (j = 1; j <= n; j++) {
    s2 += a[k][j];
  }
  for (int m = 1, x = 1, y = n; m < k; m++, x++, y--) {
    s3 += a[m][x] + a[m][y];
  }
  for (int m = n, x = 1, y = n; m > k; m--, x++, y--) {
    s4 += a[m][x] + a[m][y];
  }
  cout << s1 + s2 + s3 + s4 - a[k][k] << endl;
  return 0;
}
