Assistance with SQL View

I'm having a little trouble with this sql view.

CREATE OR REPLACE VIEW view_themed_booking AS 
SELECT tb.*,         
       CASE 
         WHEN (tb.themed_party_size % 2) = 0 THEN 
           (tb.themed_party_size-2)/2
         ELSE ((tb.themed_party_size-2)/2) + 0.5
       END themed_tables
  FROM themed_booking tb;

Can anyone help me here? I'm trying to add a column to the end of the view that the natural number result of (S-2)/2 where S is the themed_party_size.

When i say natural number result i mean like round up the answers that end in .5 so if S=7 the answer would be 3 and not 2.5.

The error I get when I try and run the above code is

Error starting at line 1 in command:
CREATE OR REPLACE VIEW view_themed_booking AS 
SELECT tb.*,         
  CASE WHEN (tb.themed_party_size % 2) = 0
    THEN (tb.themed_party_size-2)/2
    ELSE ((tb.themed_party_size-2)/2) + 0.5
  END themed_tables
FROM themed_booking tb
Error at Command Line:3 Column:34
Error report:
SQL Error: ORA-00911: invalid character
00911. 00000 -  "invalid character"
*Cause:    identifiers may not start with any ASCII character other than
           letters and numbers.  $#_ are also allowed after the first
           character.  Identifiers enclosed by doublequotes may contain
           any character other than a doublequote.  Alternative quotes
           (q'#...#') cannot use spaces, tabs, or carriage returns as
           delimiters.  For all other contexts, consult the SQL Language
           Reference Manual.
*Action:

If it makes a difference I am using sqldeveloper connected to an oracle server so I can use PL/SQL.

I think you can simplify with the CEIL() or ROUND() function:

CREATE OR REPLACE VIEW view_themed_booking AS 
SELECT tb.*,         
       ROUND((tb.themed_party_size-2)/2) AS themed_tables
  FROM themed_booking tb;

Not sure why you get that error. Perhaps it's the % operator that is not available in Oracle. This links suggests so: Fundamentals of PL/SQL. There seems to be a MOD() function though.