#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    start = (k*(k-1))+1
    sum = (k*(2*start+((k-1)*2)))/2
    return long(sum)

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