<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(void) {
  int A, R;
  cin >> A;
  R = (6 * A) * (A - 1) + 1;
  cout << R << endl;
  return 0;
}
