#!/bin/python

import sys

def sumOfGroup(k):
    start = k * (k - 1) / 2
    end = k * (k + 1) / 2
    return sum((i * 2 + 1) for i in xrange(start, end))

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