Oracle Stored Procedure - How to compare type NUMBER with intergers?

I have following stored procedure. Parameter FLAG_ passed in is only allowed to accept null, 0 or 1. But the condition checking (FLAG_ != 0 OR FLAG_ != 1) doesn't work. I guess this is because type for FLAG_ is NUMBER which include float. Is there a way to compare NUMBER to INT ?

create or replace PROCEDURE "ADD_RMV_FLAG"
(
  TEXT OUT VARCHAR2 
, FLAG_ IN NUMBER -- empty, 0 and 1 only values accepted.
) AS

BEGIN
-- input pramameters checking
IF FLAG_ is not null
THEN
   IF (FLAG_ is not null AND (FLAG_ != 0 OR FLAG_ != 1))
   THEN
     raise_application_error(-20001, 'ERROR: only empty, 0 or 1 is accepted   
     for FLAG. Passed in ' || FLAG_);
   END IF;
 END IF;
END ADD_RMV_FLAE