Question: Programming Error Message

Hi everyone, I'm new to the forum and also new to Maple.

I am trying to do the following:

"Write a procedure, marks, to take a student’s mark and output the appropriate grade, based on the following table:"

However I am having problems right from the beggining.

I have entered the following code and keep getting back an error message.

Grade:=proc(mark::nonnegative, numeric);

and this is the error that comes up:

Error, unterminated procedure

As I am quite new to Maple I don't understand where I am going wrong.

Any help at all would be appreciated, thanks :)