#include <cstdio>
#include <vector>

using namespace std;

long long Sum(long long n) {
  return n * (n+1) / 2;
}

int main(void) {
  long long k;
  scanf("%lld", &k);
  
  long long n = k * (k-1) / 2;
  
  printf("%lld\n", k + 2 * (Sum(n+k-1) - Sum(n-1)));
  
  return 0;
}