How about this:
declare @startdate datetime; set @startdate = dateadd(mm, datediff(mm, 0, getdate()), 0)
declare @days int; set @days = day(dateadd(mm, 1, @startdate)- 1)
select (@days/7) * 5
+ len(replace(substring('111110011111', convert(int, @startdate+1) % 7, @days%7), '0', ''))
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