International Math Olympiad Shortlist 2011 - C2 - A viewer suggested problem that I learned to love

I seriously disliked this problem when I first saw it, but because it was a viewer suggestion I had to look into it. I drew the problem figured out what it looked like and it's actually a pretty cool combinatorics problem. If you're a combinatorics beginner, this can look daunting because it is for beginners. Try IMO SL 2013 C1 first or start solving the problem after I translate it into some mathematical notation. If you're an intermediate combinatorics problem solver, this is a cool problem to practice on. Take the upper suggest bound of time to play with this problem. If you've done a bunch of combinatorics and consider yourself a pro (and don't consider yourself this if you haven't solved a couple of C3s, C4s, C5s), this will be nice training for you.