how to get total number of working days in a month?

WITH c AS
     (SELECT     TRUNC (sysdate, 'MM') + ROWNUM - 1 n,rownum
       FROM DUAL
      CONNECT BY ROWNUM <= (TRUNC (sysdate) - TRUNC (sysdate, 'MM'))+1)
SELECT sum(decode(to_char(n,'D'),7,0,6,0,1)) weekdays
  FROM c