#!/bin/python

import sys

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

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