#!/bin/python3

import sys

def sumOfGroup(k):
  seqn=(((k*(k+1))//2)*2)-1
  ar=seqn-2
  for i in range(k-1):
    seqn=seqn+(ar)
    ar=ar-2
  return(seqn)
if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)