#!/bin/python3

import sys

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

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