#!/bin/python3

import sys

def sumOfGroup(k):
    n=k*(k-1)//2
    start=2*n + 1
    s=start
    for i in range(k-1):
        start+=2
        s+=start
    return s

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