#!/bin/python3

import sys

def sumOfGroup(k):
    n=((k*(k+1)//2)*2)-1
    s=0
    for i in range(0,k):
        s=s+(n-(2*i))
        
    return s

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