#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, s = 0;
  cin >> n;
  if (n >= 1 && n <= 100) {
    if (n == 1)
      cout << 1;
    else {
      while (1) {
        if (n == 2) {
          s = s + 5;
          break;
        }
        s = s + (n * 2) + (n - 2) * 2;
        n = n - 1;
      }
      cout << s;
    }
  }
}
