#!/bin/python

import sys

def sumOfGroup(k):
    cl,su = 0,0
    # Return the sum of the elements of the k'th group.
    for i in range(1,k+1):
        su += i
    F_element = su * 2 - 1
    for i in range(1,k+1):
        cl = cl + F_element
        F_element -= 2
    return cl
if __name__ == "__main__":
    k = int(raw_input().strip())
    answer = sumOfGroup(k)
    print answer