#!/bin/python3

import sys

def clacK(k):
    start = 1
    return start + sum([i*2 for i in range(1,k)])

def sumOfGroup(k):
    start = 1
    K =clacK(k)
    #print("k={0} K={1}".format(k, K))
    for i in range(1,k):
        start += 2
    #print(start)        
    start = K * k + sum( [i*2 for i in range(1,k) ])      
    return start
if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)