import java.util.Random;
import java.util.TreeSet;
import java.util.concurrent.ConcurrentSkipListSet;

public class JI9029945 {

	private static volatile boolean modifierIsAlive = true; 

	public static void main(String[] args) { 
		final ConcurrentSkipListSet<Integer> concurrentSet = new ConcurrentSkipListSet<>(); 
		Thread modifier = new Thread() { 
			private final Random randomGenerator = new Random(); 

			public void run() { 

				while (modifierIsAlive) { 
					concurrentSet.add(randomGenerator.nextInt(1000)); 
					concurrentSet.remove(randomGenerator.nextInt(1000)); 
				} 
			}; 
		}; 
		modifier.start(); 
		int sum = 0; 
		while (modifierIsAlive) { 
			try { 
				TreeSet<Integer> sortedCopy = new TreeSet<>(concurrentSet); 
				// make sure the copy operation is not eliminated by the compiler 
				sum += sortedCopy.size(); 
			} catch (RuntimeException rte) { 
				modifierIsAlive = false; 
				rte.printStackTrace(); 
			} 
		} 
		System.out.println("Dummy output: " + sum); 
	} 
}