Working with dates

Hello,

I need to do the following select:

Number of days of month - weekends - holydays

So this query will return the number of days that people can work

Look that I have the holydays in one table, it's bellow:

CREATE TABLE holidays
(
id_holidays serial NOT NULL,
dt_holiday date,
holiday_description character varying(60),
input_date timestamp without time zone NOT NULL,
CONSTRAINT holidays_pkey PRIMARY KEY (id_holidays)
)

I have no idea of how do it

If someone could help, I would appreciate.

Thanks