I often see advice like “learn math” or “study number theory”, but that’s too broad.

What I actually want to know is: From your own experience, what specific math topics did you find most important between newbie → pupil (800–1200 rating)?

For example, instead of just saying number theory, please mention which part: gcd/lcm, modular arithmetic, primes, factorization, etc. Same for combinatorics, geometry, algebra, etc.

It would be even better if anyone can share stats (like how often certain math appears in problems of this range).

Please share your knowledge, Thanks for the attention!