#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    start = k*(k-1)+1
    sumk=0
    for i in xrange(k):
        sumk+=start
        start+=2
    return sumk

if __name__ == "__main__":
    k = int(raw_input().strip())
    answer = sumOfGroup(k)
    print answer