Formula Counting Days Including weekends, excluding Holidays

Hi everyone,

I am searching for a formula to count days including weekends but excluding holidays (or certain days that I can choose by putting them in a list)
When I get a document posted on a server, I need to count 30 days until I give an answer. (Lets call this the "response time") In those 30 days, weekends are included. So it's just the creation date of the document +30days. But with the christmass holidays nobody works so the end date (30days) needs to be extended . e.g. the last workday was 21/12/18 and the first workday of the new year was 07/01/19 so when a document comes in on 20/12/18 I count one day until 21/12 and I need to count 29 days after 07/01/19. And I need to put this in a formula.

Online I only find formulas to exclude weekends and holidays, or only weekends, but I can't find a formula which only exclude holidays.

Is there someone who can help me please?

Many thanks!

=WORKDAY.INTL(A1,30,"0000000",$K$1:$K$20), in KK there are holidays

Thank you very much!
You have made my day!