#!/bin/ruby

def sumOfGroup(k)
    no_elements_skipped = ((k)*(k-1))/2
    first_element = (no_elements_skipped+1)*2 -1
    last_element = first_element + 2*(k-1)
    sum = (k*(first_element + last_element))/2
    # Return the sum of the elements of the k'th group.
end

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