#!/bin/python3

import sys

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