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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 int n, i, t(1);
  cin >> n;
  for (int i = 0; i < (int)n; i++) t += (12 * i);
  cout << t;
}
