#!/usr/bin/env python

from sys import stdin, stderr

def Choose2(N):
   return N*(N-1)/2

def main():
   K = int(stdin.readline().strip())
   start = Choose2(K) + 1
   end = start + K - 1
   #print start, end
   sumrange = Choose2(end+1) - Choose2(start)
   res = sumrange*2 - K
   print res
   return 0

if __name__ == '__main__': main()