public static void atLeastOne(int n, Runnable r){
        Thread[] t = new Thread[n];
        for(int i=0;i<n;i++)
            t[i] = new Thread(){
                public void run(){
                    r.run();
                    if(!isInterrupted()){
                        for(Thread x : t)
                            if(x != currentThread())
                                x.interrupt();
                    }
                }
            };

        for(Thread x : t)
            x.start();
    }