#!/bin/python

import sys

def sumOfGroup(k):
    n=k-1
    term=((n*(n+1))/2)+1
    sum=0
    for x in range(term,term+k):
        sum=sum+((2*x)-1)
    return sum
if __name__ == "__main__":
    k = int(raw_input().strip())
    answer = sumOfGroup(k)
    print answer