Yeah I scored 100/100 in Mathematics in my class 12th ISC board and anyone from India will know how easy/hard it is to get that score. But when I entered in CP and solve some codeforces question I sucked. I mean solving even a 1000 rated problem became a struggle for, and even I never heard of word like parity I just was like odd and even but not parity. Within some months I realise it was not DSA that I was lacking, it was pure mathematics because during my enitre school journey I never learnt how to proof my own formulas or how to contradict my guess to reach an optimal state.

So i did what any normal math person will do — I learnt it. In my college I solved 9 to 10th class level olympiad questions and followed two books Mathematics Circles and Problem Solving strategies by Arther Engel. As I was already good at maths it took me few weeks to understand it and some months to really grasp it. Also solving previous year INMO previous years paper helped me a lot.

Now here I am, it takes me only 10-15 minutes to solve A and B questions of div 2 because most of the time it was just maths logic tweaked in words. So anyone who wants to be good at CP somehow must be good at Mathematics. Otherwise it will be going hard for you and ultimately you are going to quit.