Display an ad on a specific level?

Hello. My name is Cosmin and I need some help from you guys please.

I'm making a game that will have 48 levels.

My game is a physics game and I made an event sheet for all 48 levels.

I managed to implement the ad code with MobileAdvert plugin, so that the ad will run at the beginning of the level, but because I have a single event sheet for all the levels, the ad it's shown at the beginning of every level, and that is too much.

My question is that:

How can I manage to display the ads once at every 4 levels?, or even randomly?. I mean at the beginning of level 1 and at the beginning of level 5 and so on.

Thank you very much for the support.

Ok. Thank you very much. I was thinking of something like that but my idea was not very clear.

I will try like you said. Thank you again.