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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() {
  long long a;
  cin >> a;
  long long s = 1;
  int i;
  for (i = 1; i <= a; ++i) s += (12 * i - 12);
  cout << s;
  return 0;
}
