Hi Codeforces, I wanted to talk about some annoying problems I've noticed on last 2 rounds, one example is todays B, i figured out that it's about parity, but i couldn't see why a simple brute force solution will be fast enough, so i spent to much time trying to optimize it, another one is this, which is easy somehow to find the idea but i wasn't really ready to code a vast solution for it which may not work, but i decided to do it after sometime of thinking(during contest) about different optimized ways to implement it, to find after the contest that top coders just used some easy ways to avoid what i did.

What i noticed is that those two problems stick on my mind now because they was a pain, so i think now that one of the best ways to improve on competitive programming is those annoying problems.

So, if you have any other "annoying" problems like these (simple idea but hard proof, or simple idea but tricky implementation), feel free to share them in the comments. Even hard problems are welcome. They'll definitely help others, not just me.

Thanks for your time.