#!/bin/python3

import sys

def sumOfGroup(k):
    start = k * (k-1) // 2 + 1
    start = start * 2 - 1
    end = start + 2 * (k - 1)
    # print(start,end)
    b = (end + 1) // 2 
    a = (start - 1) // 2
    return b ** 2 - a ** 2

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