#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    n=k*(k+1)//2
    sum1=0
    for i in range(k):
        sum1=sum1+n*2-1
        n=n-1
    return sum1
    
    

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