Determine begin month date from month end date.

What would be the VBA code to determine the begin month date from the month end date in cell F5 AND put in a variable named BeginMonthDate.

For example:

F5 = 09/30/2005
need BeginMonthDate to equal 09/01/2005

or

F5 = 12/31/2005
need BeginMonthDate to equal 12/01/2005

Thanks a million. mikeburg