#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    start = (((k-1)*(k))/2)
    stop = ((k*(k+1))/2)
    total = 0
    for i in range(start,stop):
        total+=(i+(i+1))
    return total
        
    #t1 = sum(range(k))
    #return sum(arr[t1:(t1+k)])

if __name__ == "__main__":
    #arr = range(1,100000000, 2)
    k = int(raw_input().strip())
    answer = sumOfGroup(k)
    print answer