How do I strip the URL down to just the file name?

I have
dim dept1, filename
dept1 = Session("Dept")
filename = request.ServerVariables("URL")
filename = filename.substring(filename.lastIndexOf("//"))

I'm thinking .net and it's not working saying that i need an object on the last line.

The third line returns
/something/mypage.asp
I want to get that down to just mypage.asp

thanks
Michael Hsu