#!/bin/python3

import sys

def sumOfGroup(k):
    sumn = 0
    num = int((k*(k-1)/2)*2) + 1
    for i in range(k):
        sumn = sumn + num
        num = num +2
    return sumn

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