#!/bin/python3

import sys

def sumOfGroup(k):
    s=k-1
    n=0
    sum1=0
    while(s>=0):
        n=n+s
        s=s-1
    t=3+(n-1)*2
    for i in range(k):
        sum1=sum1+t
        t=t+2
    return sum1
        
    

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