How does the Hibernate HiLo algorithm guarantee the uniqueness of the identifier for clustered applications?

This post explains the Hibernate HiLo algorithm very well - What is the Hi / Lo algorithm?

But I don't understand how this guarantees the uniqueness of the ID for the clustered application.

For example, if the Hi number is 35, and if two clients try to increase the Hi number at the same time, what will be the Hi number each client will receive?