#!/bin/python

import sys

def sumOfGroup(k):
    odd_no=sum=0
    for i in range(1,k):
        odd_no=odd_no+i
    add=(odd_no+1)*2-1
    for j in range(k):
        sum=sum+add
        add=add+2
    return sum   
if __name__ == "__main__":
    k = int(raw_input().strip())
    answer = sumOfGroup(k)
    print answer