Budget fitness watch

Never owned any kind of smart\fitness watch so know exactly zero things about them. I'm on a very tight budget, but also don't need big functionality. My only reqs are:

1. Tracks steps
2. Counts calories (this one is the most important)
3. Optional, but would be nice for it to be waterproof

Everything else doesn't matter to me much. I also have an iphone, but I don't think there's any major benefit for me in the watch being compatible with it.