RIGHT functionality without using builtin RIGHT function

CREATE FUNCTION dbo.RightValues

(

   @InputString   NVARCHAR(MAX)

   ,@RightValues  INT

)

RETURNS NVARCHAR(MAX)

AS

BEGIN

   DECLARE  @Count   INT = 0

            ,@Len    INT

            ,@Output NVARCHAR(MAX) =''

   SET @Len = LEN(@InputString)

   IF @Len < @RightValues

   BEGIN

      RETURN NULL

   END

   ELSE

   BEGIN

      WHILE (@Count < @RightValues)

      BEGIN

         SET @Output = SUBSTRING(@InputString, @Len-@Count,1) + @Output

         SET @Count = @Count + 1

      END

   END

   RETURN @Output

END

SELECT dbo.RightValues('abc',4)