3 Criteria of certain dates

I have a date list in column A that is constantly updating with today's date via a macro.

What I am trying to do is input a "simple" if formula in the B column by all the dates so that it places a "5" next to the specific date.

Three criteria define the specific date :
1. Only once a month a "5" need to be in column B next to the date.
2. A "5" is placed when a day is 4th day of the month or if there is not a 4th day very the next day.
3. If there is any repeat rows with the 4th day, only put a 5 next to the 1st occurrence.

4/1/2012
4/2/2012
4/3/2012
4/4/2012 5
4/5/2012
4/6/2012
4/7/2012
4/15/2012
4/21/2012
4/26/2012
5/1/2012
5/5/2012 5
5/11/2012
5/19/2012
5/25/2012
6/2/2012
6/4/2012 5
6/4/2012
6/4/2012
6/5/2012
...

Can you help me out ?
Thx, John

Perfect. Thank you. I meant to input a formula and not by VBA anyway.