//RecursionDemo2.java

import java.util.Scanner;

public class RecursionDemo2
{
    public static void main(String[] args)
    {
        System.out.println("Enter a nonnegative number:");
        Scanner keyboard = new Scanner(System.in);
        int number = keyboard.nextInt();
        System.out.println(number + " contains "
            + getNumberOfZeros(number) + " zeros.");
    }

    /**
     * Precondition: n >= 0.
     * Returns the number of zero digits in n.
    */
    public static int getNumberOfZeros
    (
        int n
    )
    {
        int result;

        if (n == 0)
            result = 1;
        else if (n < 10)
            result = 0;  //n has one digit that is not 0
        else if (n % 10 == 0)
            result = getNumberOfZeros(n / 10) + 1;
        else //n % 10 != 0
            result = getNumberOfZeros(n / 10);

        return result;
    }
}