#!/bin/python3

import sys
if __name__ == "__main__":
    k = int(input().strip())
    p=0
    l=k
    for i in range(0,k):
        p=2*i+p
    p=p+1
    sum=0
    for i in range(0,l):
        sum=sum+p
        p=p+2
    print(sum)