#!/bin/python

import sys

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

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