autofill on fixed dates

[Guido Cole]

In colum A I have a series of dates, in C1 I have a fixed value. I want this
value to appear in colum B on each 15th and 30th of the month. How can I
programm the function in colum B?

Thanks for any help.

Guido

 

[David Biddulph]

=IF(OR(DAY(A2)=15,DAY(A2)=30),C$1,"")