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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 n, res = 0;
  cin >> n;
  for (int i = n; i >= 2; i--) res += (12 * (i - 1));
  res += 1;
  cout << res << endl;
  return 0;
}
