<image>

Input

The input contains a single integer a (1 ≤ a ≤ 18257).

Output

Print a single integer output (1 ≤ output ≤ 2·109).

Examples

Input

2


Output

13
#include <bits/stdc++.h>
using namespace std;
int main() {
  int a;
  cin >> a;
  int output = 0;
  int an = 12 * (a - 1);
  output = an / 2 * a;
  cout << output + 1;
  return 0;
}
