[O] export to beamer with heading 1 as separators

[Luca Ferrari]

Hi all,
I'm trying to export to beamer my org-mode presentation, but I would
like that top level elements in the tree appears as "separators"
slides, that is chapter introduction.

So if my tree is:

* License
* Arg 0
** slide 1
** slide 2
** slide 3
* Arg 1
** slide 4
** slide 5
** slide 6

I want to have "License", "Arg 0" and "arg 1" as slides with title on
the center (if possible).
What directive should I use?

Thanks,
Luca