/**

lazy version, 

but inefficient when called multiple times

and not really quicker than Sieve1 anyway 
(can you see why?)

so probably Sieve1 should be the preferred version

 */

import java.util.*;

public class Sieve2 {
    private BitSet primes;

    public Sieve2(int n) {
	primes = new BitSet(n);
	for(int i = 1; i < n; i++) 
	    primes.set(i);
    }

    public Enumeration elements() { 
	return new SieveEnumeration();
    }

    public class SieveEnumeration implements Enumeration {
	private int index = 1;

	public boolean hasMoreElements() {
	    int n = primes.size();
	    for(int i = index+1; i < n; i++) 
		if (primes.get(i)) {
		    if (i*i < n) 
			for(int j = 2*i; j < n; j += i)
			    primes.clear(j);
		    index = i;
		    return true;
		}
	    return false;
	}
	
	public Object nextElement() { return new Integer(index);}
    }



    public static void main(String[] args) {
	Sieve2 p = new Sieve2(Integer.parseInt(args[0]));
	Enumeration primes = p.elements();
	primes = p.elements();

	int count = 0;
	while ((primes.hasMoreElements()) &&
	       (((Integer) primes.nextElement()).intValue() < 42))
	    count++;
	System.out.println(count + " of these primes are smaller than 42.");
    }
}