#!/bin/python

import sys

def sumOfGroup(k):
    startN = 1 + ((2 + (k - 1) * 2) * (k - 1)) / 2
    endN = startN + 2 * (k - 1)
    return ((startN + endN) * k) / 2

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