#!/bin/python

import sys

def sumOfGroup(k):
    start = 1
    for i in range(1,k):
        start += (2*i)
    #print start
    start *= k
    #print start
    for i in range(1,k):
        start += 2*i 
    return start

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