How do I deal with these bullies on the train station?

Alright, so they look like they're in middle school, and while I'm a junior in high school they seem to have no problem picking on me. Before today, they'd just scream at me and start laughing hysterically, which I just ignored. But today as soon as they saw me they started saying "oh here's the chink" and started throwing rocks at me. And these are just random people that I've NEVER met in my life before. So my question is what do I do? I'm not scared of them and I'll probably talk back if they do the same thing tomorrow but I'd rather not have this turn into a fight and get the police involved (obviously). So...yeah. And it's 2 girls and a guy too so the odds are kind of against me if I DO get into a fight.