#!/bin/ruby

def sumOfGroup(k)
    # Return the sum of the elements of the k'th group.
    index = (k*(k-1))/2
    first_odd = index*2 + 1
    total = 0
    count = 0
    k.times {
        total = total + first_odd+(2*count)
        count = count + 1
        }
    return total
end

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