#!/bin/python3

import sys

def sumOfGroup(k):
    sum1=0 
    n = (int)(((k-1)*(k))/2)
    a = 1+(n*2)
    for i in range(1,k+1):
        sum1+=a
        a+=2
    return sum1


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