HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

I have mod 3.35... the number of lizards in the castle is calculated incorrectly... it should show that you can buy 9, or at most 18... but it shows 16.

At the time of writing this post, version 3.36 has already been released, which fixes this issue.
Check the box for "check for updates every time the game starts" in the launcher.