I want to start learning olympiad mathematics more seriously, and I would like to have advice on some good books or pdfs to learn with.
I have background but not a big background. For example I know high school geometry (and in general high school mathematics) really well but in olympiad geometry (where creativity is really needed) I am not that good. I can solve a bit of the problems from the national math olympics in my home country but not problems from the IMO (though I can understand the solutions of the easier problems in the IMO, mostly easier geometry problems).
Right now I want to focus mainly on geometry and number theory, and maybe some combinatoris. Are there any books that are really recommended for a beginner (not a beginner who starts from absolute scratch, but still a beginner).
I heard about the book "Euclidean geometry in mathematical olympiads" written by Evan Chen but I understood that this book is advanced and a beginner should not start from that.
Any good books to begin with in geometry, number theory, and combinatorics (and if you have anything else to recommend on - for example a good Algebra book to begin with when I'll start learning algebra - of course I would like to hear it as well).
If you have any advice on math olympiad in general, or if you think I should learn something else first (for example if you think I should learn algebra before number theory) - please tell me.