Flush the   keyboard   buffer.

This reads characters from the keyboard input and
discards them until there are no more currently buffered,  
and then allows the program to continue.

The program must not wait for users to type anything.

with Ada.Text_IO;
procedure Flushtest is
   use Text_IO;
begin
   Put_Line ("Type anything for 2 s");
   delay 2.0;
Flush_Input:
   declare
      Ch   : Character;
      More : Boolean;
   begin
      loop
         Get_Immediate (Ch, More);
         exit when not More;
      end loop;
   end Flush_Input;
   New_Line;
   Put_Line ("Okay, thanks. Here is some input from you:");
   Put_Line (Get_Line);
end Flushtest;