EXCUSE ME, GUYS !
i forgot to add one monome:
7*(((to_char(date_trunc('month',now()),'D'))::INT2-1)/4)
which is stands for skip a first week of month in case it is not consist Wed
finally the select will be similar the following
SELECT 7*(((to_char(date_trunc('month',now()),'D'))::INT2-1)/4) + 1 -
(to_char(date_trunc('month',now()),'D'))::INT2 + 7*3-3 ;
4 - is a number of Wed in a week (in postgresql numeration)