Remove Controller from the URI to keep URL Shorter

[eluser]Unknown[/eluser]
Hello.

I want to keep the url's short and have this:

www.example.com / function / ID

so that by default my controller called Main will accept the functions.

My question is:
How can I do this so that I do not have to re-edit the routes.php file when I add another controller?
e.g. in three months time I decide to add an Admin controller

To add
I have my Main controller accepting the functions currently. I'm doing the following which I found here

Code:

$route['^(?!exemptdomians|ezsell|login).*'] = "main/$0";

But this means I have to re-edit this in routes.php whenever I add a controller.

many thanks if you can give any help!