DECLARE
   	Str VARCHAR2(20) := '&Str';
	Rev_str VARCHAR2(20);
   	len INT;
   	ctr  INT;
BEGIN
	len :=LENGTH(Str);
   	FOR ctr IN REVERSE 1..len LOOP
         	Rev_str:= Rev_str ||SUBSTR(Str, ctr, 1);
   	END LOOP;
	DBMS_OUTPUT.PUT_LINE(Rev_str);
END;