Event system for collecting

I am trying to create a action game type of thing kinda like a beyonetta or darksider. In my game i have set up side things like hidden objects and if you find them it activates a sequence of special events. I got that figured out but my problem is I don't know how to get the game to count how many the player activates. I want to set it up like a level may have 4 of them and if you find all 4 at the end of the level you get a reward. How can I set this up using events?/

Create it with variables. Each time the player activates one of them add a +1 to that specific variable. Then create a event where the variable is equal or higher than 4 and put in a conditional branch where you will get the reward if the variable is complete.

If you want some more help with setting it up, I can try and write something down for you