using System;

public class Program

{

    /* Recursive Multiply: Write a recursive function to multiply two positive integers without using

    the * operator (or / operator). You can use addition, subtraction, and bit shifting, but you should

    minimize the number of those operations. */

    public static int RecursiveMultiply(int num1, int num2){

        var smaller = Math.Min(num1, num2);

        var bigger = Math.Max(num1, num2);

        return RecursiveMultiplyHelper(smaller, bigger);

    }

    private static int RecursiveMultiplyHelper(int smaller, int bigger){

        if (smaller == 0) return 0;

        if (smaller == 1) return bigger;

        var newSmaller = smaller >> 1; //divide by 2

        var halfProd = RecursiveMultiplyHelper(newSmaller, bigger);

        return (smaller % 2 == 0) ? halfProd + halfProd : halfProd + halfProd + bigger;

    }

    public static void Main()

    {

        Console.WriteLine(RecursiveMultiply(20,9));

    }

}