#!/bin/python3

import sys

def sumOfGroup(k):
    n=k*(k-1)+1
    sum=0
    for c in range(k):
        sum+=n
        n=n+2
    return sum
        
        
   

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