Thread management

What is the maximum number of threads that can work concurrently in the program below?

SlackerThread is a class representing a thread that sleeps a random number of seconds after the start.

Tip: Don't forget about the main thread.

public class Main {
    
    public static void main(String args[]) throws InterruptedException {
        Thread t1 = new SlackerThread();
        Thread t2 = new SlackerThread();
        
        t1.start();
        t2.start();
        
        t2.join();
        
        Thread t3 = new SlackerThread();
        Thread t4 = new SlackerThread();
        
        t3.start();
        t4.start();
        
        t3.join();
        t4.join();
    }
}