URL method

[eluser]Dr. x[/eluser]
hi every one. am new here on codeigniter and glade for that, so many thanks for all it's team work.
am covert from already building script into MCV and i know hot to make the url same to "class/function/id" but i want to make small modification to the url to be as that
"class/function/constant_id" so the variable that will pass to the function is only $id not constant_id
i will appreciate for any help
and so sorry for my english
Best Regards