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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 a[19000];
int main() {
  int ans = 1;
  int n;
  cin >> n;
  int cur = 12;
  for (int i = 1; i < n; i++) {
    ans += cur;
    cur += 12;
  }
  cout << ans;
  return 0;
}
