Input form in CAS programs

[Tonig00]

When I introduce a simple program like:

#cas
PPP2():=
BEGIN

LOCAL a;

INPUT(a);
PRINT(a):

return 0;
END;
#end

It gives me an error: "Error: Invalid input"
This simple program works in NON CAS program, so why does not work in CAS?

Thanks in advance to anyone who answers me