#!/bin/python

import sys

def sumOfGroup(k):
    t=(k*(k-1))/2
    a=2*t+1
    b=2*(t+k-1)+1
    s=0
    for i in xrange(a,b+1,2):
        s+=i
    return s

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