#!/bin/python

import sys

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

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