SQL & PL/SQL :: Week On Particular Day According To Arabic Calendar

As my requirement is that to find week for particular date according to Arabic calender.As per Arabic calender first day for year starts from saturday.

so when i execute query :

select to_char(to_date('05/26/2013','MM/DD/RRRR'),'WW')
from dual;

Then it gives 21,but as per arabic calender it should show 22nd week.

getting result according to Arabic calender as it should return 22,because weak starts from saturday according to Arabic calender.