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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;
  if (a == 1) {
    cout << 1;
    return 0;
  }
  cout << (a - 1) * a * 6 + 1;
}
