Ab Workout Help? Read For Somewhat Further Details…?

Hey guys!! I hope all of you are doing well today and can actually help me. I have tons of summer reading to do for my senior HS year! I love laying down on my comfy green couch, but I hate building on my belly fat. I usually like eating celery sticks, ice cream, and such while I’m reading, also.

So, I was wondering if there was any ab workouts I can do at home that mainly require:
-A lying or sitting position
-Not that many changing positions (i.e., no change in position every 10 seconds or something….more like every page)
-Won’t let me lose my concentration
-Must be TOTALLY FREE…I don’t want to have any fancy machines or anything like that.

Thanks a LOT everyone!!! <3