#!/bin/python

import sys

def sumOfGroup(k):
  k -= 1
  n = k * (k + 1) / 2
  hi = (n + k + 1) * (n + k + 1)
  lo = n * n
  return hi - lo

if __name__ == "__main__":
  k = int(raw_input().strip())
  answer = sumOfGroup(k)
  print answer