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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 a, result = 1;
  cin >> a;
  for (int i = 1; i <= a; i++) {
    result = result + (i - 1) * 12;
  }
  cout << result;
}
