COUNTIF based on condition from 2 columns

Hello,

I have the following situation:

I need to count how many times a key work appears on a column, based on condition from another column...

Example:
A B
q w
q y
a w
z w

I need to count how many times "w" appears in col B when col A value is "q". (so the result would be 1 to the above example)

I tryed a COUNTIF:
=COUNTIF(AND(B1:B4;"=w"; A1:A4="q"))
but of course the formula is not correct.

Please advise...