#!/bin/python

import sys

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

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