#!/bin/python3

import sys

def sumOfGroup(k):
    j=k*(k-1)-1
    summ=0
    for i in range(k):
        j+=2
        summ+=j
    return summ
    # Return the sum of the elements of the k'th group.

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