#!/bin/python3

import sys

def sumOfGroup(k):
    if k==1:
        return 1
    p = int(k*(k-1)/2)
    pp = 2*p + 1
    s = 0
    for i in range(k):
        s += pp + 2*i
    return int(s)

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