#!/bin/python

import sys

def sumOfGroup(k):
    skips = 0
    cur = 1
    for i in range(k):
        cur += 2*i

    result = 0
    for i in range(k):
        result += cur
        cur +=2
    return result

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