#!/bin/python3

import sys

def sumOfGroup(k):
    start = ((k-1)*(k)) // 2
    end = (k*(k+1)) // 2
    return pow(end, 2) - pow(start, 2)

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