#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    #identify the range of index  for kth bracket
    if k < 1 :
        return
    ptr = ((k-1)*k)/2
    ptr = 2*ptr + 1
    sum = 0
    for i in range(k) :
        sum += ptr
        ptr += 2
    return sum

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