#!/bin/python3

import sys

def sumOfGroup(k):
    s = 0
    # Return the sum of the elements of the k'th group.
    for i in range(k*(k-1)+1,k*(k+1),2):
        s+=i
    return s

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