Two Inlets of numbers boxes, alternating to one outlet

Hi folks,
I can't imagine, that the thing I want to do is very difficult. Nevertheless I'm occupied for many hours with it now. I hope somebody can help me with my problem.

I have two numbers boxes (numbers box 1 and numbers box 2), that have changing numbers alternating. I want to use alternating the output of "numbers box 1" and "numbers box 2", always prefering that box that has changing numbers at the moment and give the information into a Filtergraph.

The Problem I got is, that a numbers box has always an output, doesn't matter if there is a changing number or a stored number on it's output. And if there are two numbers boxes giving their output to the inlet of the same filtergraph, there is a kind of conflict, because there are two different numbers at the same time on the inlet of a filtergraph. So what I need is some kind of patch or box or whatever, that takes the numbers of both numbers boxes (numbers box 1 and numbers box 2), chooses always the one that has a changing number at the moment it brings the filtergraph.

In any case, thank you very much.
atb Merlin