Help for %SystemDrive% Dir

Hi, the answer is very simple, maybe, but I'm new.
How to obtain the% SystemDrive% location.

I coded this but is it okay?

SystemDrive = String.Left(_WindowsFolder, 3)
if String.Right(SystemDrive, 2) == ":"..String.Char(92) then
Dialog.Message("", SystemDrive)
end

message result: C:\