#!/bin/python3

import sys

def sumOfGroup(k):
    n1=(k*(k-1))//2
    n2=(k*(k+1))//2
    sum1=(n1*(2+(n1-1)*2))//2
    sum2=(n2*(2+(n2-1)*2))//2
    return sum2-sum1

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