Recently, I have started solving 1500 rated problems, then I encountered this problem PROBLEM: Codeforces Round 962 (Div. 3) FUN link

I want to balance my Ad Hoc kind of reasoning with the maths logic as well.

The problem is that the math tag on Codeforces is a massive grab-bag. When I filter by it, I mostly get: 1. Simple pattern-finding/observation problems. 2. Standard Number Theory (primes, GCDs) that I already know or can easily learn.

Finding problems that require algebraic manipulation, variable bounding, and combinatorics is very hard. So, how can I found these problems?

Also, what should be my approach to improve well?