#!/bin/python

import sys

def sumOfGroup(k):
    n = k - 1
    kk = n * (n + 1) / 2
    m = 1 + (kk -1) * 2
    return sum(m + i * 2 for i in range(1, k +  1))

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