#!/bin/python

import sys

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