What's a good iOS game for keeping my mind sharp during study hall when the kids are just… well, you know?

Okay, so, Daily Mahjong Match. I downloaded it a few weeks ago after my students showed me—they're always on their phones, might as well learn something from it, right? It's a digital version of Mahjong, which I remember playing with my grandma. It's surprisingly intuitive, even I could figure it out after a few tries. It’s good for those moments when you need a little mental break but still want to keep your brain engaged. Think study hall when half the class is pretending to study and the other half is… well, you know. It's a good way to pass the time without getting too distracted. Plus, it's a nice change of pace from grading papers. It’s not going to win any awards for graphics or anything, but it’s solid and does the job. I’d recommend giving it a shot if you need something to occupy your mind for a few minutes here and there.