Function that returns the number of a given day of the week in a given month

Hello,

I am looking for a function that would allow me to know the number of a given day of the week in a month.
Assuming that this function is: NbJSMois
and that we had the days of the week as follows:
Monday = 1, Tuesday = 2, ..., Sunday = 7

Eg. NBJSMois (4, 1, 2009) = 5

There are 5 Thursdays in effect in January 2009.

Thank you for any response.

If you have the day of week in A1, month in B1 and year in C1 then this formula will give the number of days

=4+(DAY(DATE(C1,B1,35))<WEEKDAY(DATE(C1,B1,0)-A1))

At last I get it!

Short & nice!