url issue

[C# Programming]

I have a webpage displaying some information based on the querystring.
i.e., http://www.mywebsite.com/userdetails.aspx?userid=15510
The issue is, i want to access the information of the user while giving the url as http://www.mywebsite.com/15510
I don't know how to do that.Can anyone suggest how to achieve it?
TIA.