using System;

public class Program

{

    public static void Main()

    {

        //Hannah Zavala

        int x;

        int num = 3;

        Console.WriteLine("3, 9, 21, 45...");

        Console.WriteLine("What position of the previous series would you like to know?");

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

​

        for (int i = 1; i <= x; i++)

        { 

            num = 2*num + 3;

        }

​

        Console.WriteLine(num);

​

    }

}