Set page size in LO Impress?

How can I set the page size with LO Impress?

       There's a Page option under Format in LO Writer and Calc, but I can't find one in LO Impress. In LO Draw, Format has a "Page/Slide properties" option.

       I'm making a poster presentation at a conference, and I need to produce one PowerPoint slide that's 36.5" wide and 20.5" high. The conference has computers with MS Office loaded plus a reader for Adobe Portable Document Format (PDF). However, when I exported my *.odg file from LO Impress to PDF, it looks like it lost that size information, though I'm not sure -- and I don't know if I can find out until shortly before my presentation!

       Thanks,
       Spencer Graves
p.s. I'm using LO 5.1.4.2.

p.p.s. I'm using LO 5.1.4.2 under Mac OS X 10.11.6. Secondarily, LO Draw is shockingly slow on this machine. I have to wait several seconds for it to do almost anything. This is on a MacBook Pro that's quite fast for virtually everything else I do. Thanks.

In an Impress session (start a new one and copy from initial attempts).
1. Set your slide Layout to blank.
2. Point to the Slide and open its Context menu
3. Select the Page Properties dialog
4. Set the Paper format Width and Height as needed -- the Format field will
change to "User"
5. Set orientation and margins as preferred.

When saving the ODF document the size will be retained. Also when exporting
to PDF.

Can do similar from Draw, or Writer depending on how you'd like to layout
your poster.

Enjoy.

In an Impress session (start a new one and copy from initial attempts).
1. Set your slide Layout to blank.
2. Point to the Slide and open its Context menu

       Thanks. I had a hard time finding the Context menu. For others who might read this thread in the future, I will document here how I found it: Rt-click (Ctrl-click on my Mac) in the slide [not in the slide thumbnail on the left] -> "Format slide...". This has page width and height options.

3. Select the Page Properties dialog
4. Set the Paper format Width and Height as needed -- the Format field will
change to "User"
5. Set orientation and margins as preferred.

When saving the ODF document the size will be retained. Also when exporting
to PDF.

Can do similar from Draw, or Writer depending on how you'd like to layout
your poster.

       Draw is painfully slow for me on my MacBook Pro. Virtually everything else runs shockingly fast, especially compared the computer I replaced with the MacBook. I'm running LO 5.1.4.2 under Mac OS X 10.11.6. I rarely use Draw, in part because it's been painfully slow for me in the past, if my memory is correct.

       Thanks again,
       Spencer Graves