How do you get chalk off of limestone?

Hi, my house got TPed as an initiative to being on the drumline (the tradition is to TP the freshman's houses) and so they also wrote on the limestone (I think they thought it was concrete) with chalk and I have to clean it off. What's the most effective way to get it out and what should I use?

Thanks so much, I need to figure out the best way to do this so my parents don't kill me @__@