#!/bin/ruby

def sumOfGroup(k)
    how_many_numbers_were_before = (k*(k-1))/2
    first_element_of_group = how_many_numbers_were_before*2+1
    sum = 0
    x = first_element_of_group
    last_element_of_group = first_element_of_group + 2*(k-1)
    while x <= last_element_of_group
        sum += x
        x += 2
    end
    return sum
end

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