Skying and Aristophane

A friend of mine invited me to go skying with him (and a bunch of others guys) this weekend. I'd be very happy to go there, but my school organizes a trip to Milan to see Aristophanes's comedy "The Birds", which is wonderful, and which I probably won't be able to see another time. So I really don't know what to do. Any advice (given before Thursday) would be very welcome.