Distinct count over multiple tables

Hello Experts,

I have a situation where I need to calculate UNIQUE NUMBER OF ENGAGED USERS.

In my data model people can:

• sumbit an idea
• like an idea
• comment an idea

All of these activities are in diffrenet tables as follwoing image:

What I need is to calculate that number of unique numbers who were engaged. It means they have sumbited an idea / commented / liked.

If I filter on 1 idea I want to see if the somebody who sumbited and idea and at the same time liked and commented was calculated only once.

Please see following example for selection on IDEA = 1

Number of engaged users should be only 3.  You can see eventhougt user A has been interacted 3 times he counts only 1 time.

I was thinking to somehow virually union all 3 tables together and then run DISTINCTCOUNT. But still it has to follow the filter context.

Thanks for your help

Cheers!

Martin-Prague