#!/bin/python3

import sys

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

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