#!/bin/python3

import sys

def sumOfGroup(k):
    n=((k*(k-1))//2)
    n=2*n+1
    res=0
    for i in range(k):
        res+=n
        n+=2
    return res
if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)