How to disallow node editing at the same time by several users?

By default, two or more people can edit the same node at the same time. Only after you click "Save", you get a warning, that node is being edited by another user. That's very inconvenient. Let's say, two people are translating the same node at the same time. They spend hours on translation, and then someone gets a warning, that node is being edited by another user. Pity, isn't it?

So, how is it possible to prevent nodes from being edited by several users at the same time? It means getting a message not after you click "Save", but right after you click "Edit" or "add translation".