Category of current archive AND parent category

I’m trying to achieve something that sounds pretty easy to understand, but… whatever I do, it doesn’t work. Let me explain it :

In my archive template, I want to display the name of the current category. That’s easy and I can do that.
But I also want to display the parent category name, if there’s one.
And… I don’t want to display the category name twice when the current category is a top level one.

Thanks a lot for your help !