#!/bin/ruby

def sumOfGroup(k)
   nk = 0
   i = 0
   
   while nk < k  - 1
     nk = nk + 1
     i = i + nk
   end
   (i..i+nk).map{|x| 2*x + 1}.sum
end


k = gets.strip.to_i
answer = sumOfGroup(k)
puts answer