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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 n;
int main() {
  scanf("%d", &n);
  printf("%lld", (long long)6 * (n - 1) * n + 1);
  return 0;
}
