#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    elementsSoFar = ((k-1) * k)/2
    #print elementsSoFar
    startElement = 2 * elementsSoFar + 1
    #print startElement
    i = 0
    sum = 0
    while i < k:
        sum += startElement
        i += 1
        startElement += 2
    return sum

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