After round I saw some interesting links in the comments.

**Problem C**: https://www.quora.com/What-is-the-radius-of-the-circle-surrounding-a-circle-if-all-the-surrounding-circles-are-equal

**Problem F**: After understanding that you must find "subset with maximum XOR" on range from L to R, this subtask is becoming very easy to google it (e.g https://www.geeksforgeeks.org/find-maximum-subset-xor-given-set/)

Actually the **SAME** problem: https://blog.csdn.net/ShadyPi/article/details/79939990

You can see many accepted submissions with this idea :|

**Problem E**: https://www.geeksforgeeks.org/assign-directions-to-edges-so-that-the-directed-graph-remains-acyclic/ the same idea to direct edges in order to topological sorting.

*Thanks to Rinne and M_H_H_7 for the links in the comments* (https://codeforces.com/blog/entry/64495?#comment-484476, https://codeforces.com/blog/entry/64495?#comment-484418).

A bit notorious.

It would be useful to enclose the spoilers in spoiler tags.

Are you mad or what . see the submissions of e and f during the contest .. from 3000 in 3 to 150 in f/e. many didnt know how to come up with then idea of problem e and f. the questions were totally new to them . many people get to learn a lot from this round. whats ur problem . if u are so legend in programming why u cant defeat petr in topcoder open or gennady in gcj . or atleast in any round.

naa jante ho to bakaiti na pela karo samjhe.

We have discussed the problem D with similar constraints (actually, they doesn't matter) in our math training session. Also, the solution was exactly the same as the tutorial.

I found the link while writing this comment, check 091 here: http://olympiads.win.tue.nl/imo/soviet/RusMath.html

Maybe it is only my problem, but why are you trying so hard to google the problems? Both C and E are faster to solve by yourself than find the solution on the internet.

About F: article from geeksforgeeks doesn't tell you how to solve the problem (maybe its because geeksforgeeks is trash? idk). There are some words about Gaussian elimination but I don't think that you can understand that unless you already know that XOR is sum of vectors in . And about the same problem — it is in Chinese! Do you think that problemsetters must learn Chinese? Even the guy who wrote the original comment about that problem existence mentioned that it is 100% coincidence.

About D from comments: the problems are not the same. This is how problemsetting works: you take something already existing and change it to get new problem.

Problems are same, actually. The ASU problem is solved by finding the algorithm.

Rooks are moving by chess rules instead of jumping to any point. This one is enough for problems to be different. Algorithms maybe the same, but the proofs that it works are different.

I didn't google this problems. Links were in the comments.

The fact remains. Person who is not able to solve this problems can simply google them.