#!/bin/python3

import sys

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

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