#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    n = k*(k+1)
    n -= 1
    sum = 0
    while k > 0:
        sum += n
        n -= 2
        k -= 1
    return sum

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