How can I count the objects on a photo with "almost" the same area or radius?

I would like to make a program what can count my money. And this is where I am now:

This is my code so far: http://pastebin.com/8gpJZk3y

I know how to choose the smallest or the third biggest etc..., but I don't know how to count the circles with the same radius. So than I could count how much money we have on the image.