PDF Page count and finding halfway point and adding marks

[CruzinCooler]

Any help please would be appreciated.
Is there a way to find the half way page count in a PDF? I need to add press marks at the half way count and also round up to the count if its not an even page number.
Example if the page count is 100, I will add press marks at page 50. (Halfway and an even number)
If the page count is 103, I will add press marks at page 52. It must be an even number. (51.5 is half of 103 so rounded up to an even number would be 52).
I could always add a blank at the end of the doc to get an even page count, find the halfway point, add press marks and then remove the last page if that an easier solution to finding the halfway mark.
Thanks for any help.