#!/bin/python

import sys

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

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