using System;

public class Program

{

    public static void Main()

    {

        //Luis Salazar

        int total = 4;

        int total2 = 0;

        int x = 9;

        Console.WriteLine("4, 13, 31, 67... ");

        Console.WriteLine("From the previous series, what position would you want to know?");

        int pos = int.Parse(Console.ReadLine());

        if ( pos == 1)

        {

        Console.WriteLine("4");

        }

        else if( pos == 2)

        {

        for(int i = 2; i <= pos; i++)

        {

        total = total + x;

        }

        }

        else if( pos > 2)

        {

        for(int i = 3; i <= pos; i++)

        {

        int y = x * 2;

        total2 = 13 + y;

        }

        Console.WriteLine(total2);

        }

    }

        }