Count unique days within month

hi,

i need for my analyses number of unique days within a month:

column B - dates (some days are missing, some days have 20 lines, some have 1 line)
column C - =Month(Bx)

I need to count number of days within given month.

to count all unique days, i use this:
=SUM(IF(FREQUENCY(INPUT!B15:B2000;INPUT!B15:B2000)>0;1))

how do I add the condition IF Cx=8 ?

thanks,
Jirka