div2 B and Cis too hard

That's because you might know the answer of the questions after the end of contest. So, if you want to increase your rating, please registered for rated before the contest is started.

How do you know that before the contest???

hope to finish D and E to increase my rate

In fact, you should buy as less as you can in one deal. but, the limit of k makes you must make some large deals. So, you should use as less as you can deals to fit the limits by greedy. and an important step is to find out that break a great deal is better than break a little deal.So you break the largest deal into three small deal and the count of deal plus 2.Repeat it untill reach the limit

please tell me where to hack others code?I hadn't use this function before.Thanks

I can't agree more.In fact,testing this kind of code is really easy.Just put a piece of code made by AI on the against-cheating platform can test it out.However,many of the newcommer have the ability to finish problem E.they may ranked high on Luogu,Atcoder or other OJ platform

I solved 2 questions at last,and ranked 8626.I think it's a good result for a beginner.btw,I don't know how to participate in div3or4,I can only find div1 or2 in the contests page

thank you.

It is my first game in codeforces.I hope that I will pass at least 1 question.I don't know how hard the questions because I am a beginner of computer science.Good luck for me.