class VClock {

    public void merge(VClock other) {
        for (Map.Entry<String, Long> clock : other.vc.entrySet()) {
            Long time = this.vc.get(clock.getKey());
            if (time == null) {
                this.vc.put(clock.getKey(), clock.getValue());
            } else {
                if (time < clock.getValue())
                    this.vc.put(clock.getKey(), clock.getValue());
            }
        }
    }

    public  VClock();

}