#!/bin/python3

import sys

def sumOfGroup(k):
    k -= 1
    x = (k*(k+1)) // 2
    y = 2*(x+1) - 1
    r = 0
    for i in range(k+1):
        r += y
        y += 2
    return r

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