Hello everyone, this winter at Petrozavodsk was my first ICPC contest, now it is loaded on the gym.

To ensure Codeforces traditions, I will say thanks to the testers TLE, whzzt, sunset, wxhtxdy, isaf27. Also thanks to izban with help in tasks choosing.

And of course, thanks to MikeMirzayanov for Codeforces and Polygon platforms and help with loading this contest to the gym.

**A, Short editorial**

**B, Short editorial**

**C, Short editorial**

**D, Short editorial**

**E, Short editorial**

**F, Short editorial**

**G, Short editorial**

**H, Short editorial**

**I, Short editorial**

**J, Short editorial**

**K, Short editorial**

editorial?

here it is

most of the students in China can't visit *.google.com

so could you please provide another one in other dropboxs like onedrive?

thanks a lot ^_^

For I do you mean to say that for any biconnected component has size at most 6 because otherwise the result is wrong for a tree of 7 vertices?

No, any connected component. And it is true, probably you misread the statement.

So if I have a tree on 7 vertices + 1 additional isolated vertex and I set A=set of vertices of the tree. Then, there does not exist a,b in A such that any path from a to b pass through the isolated vertex?

There exists another subset, which violates the constraint.

Can someone explain the solution for problem D with Hall's Theorem? Didn't get in the tutorial.