#!/bin/python

import sys

def sumOfGroup(k):
    n=k*(k-1)+1
    i=0
    sum1=0
    while i<k:
        sum1+=n;
        n+=2
        i+=1
    return sum1
            
        

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