So today I encountered an interesting math task that I would like to share with you:

There are 2 old men and 16 stones. All stones are coloured in 4 different colours, there are 4 stones of each colour. 2 men play game: each round they randomly pick 1 stone from the pile, after every round they switch turns. The game ends in victory, if one of the men has gathered 3 stones of the same colour, otherwise it's a draw. The task is to calculate the probability of the game ending in victory.

Now, I already know the answer for this problem, but I would love to see how cf community is gonna solve it, cause there's 1 detail about this problem that I consider interesting. I'll share it after some answers.

Hi! I have a question: when you solve a hard (higher than your rating) problem during contest, but at the same time lose your rating, do you consider it a success?

So lately me and my friend were discussing a certain take on "debugging" game-theory or interactive problems. Basically, you come up with solution, if you're not sure with it, you can use the strategy you came up with to play game with GPT or any other person available. You don't ask them for solution, just explain the rules of the game and thus test your strategy. So we're kind of interested, is it listed as illegal/should be considered illegal here on cf?

I think someone might be abusing tags feature:

I've always thought than all NK accounts are fake and made by trolls, but then I checked last div2 standings and found this:

Then I checked other NK accounts and found out that they all have this strange, but yet similar names, and also 0 comments and blogs. And it looks like they're pretty good at CP apparently. So could this be the real North Korean participant? And might they be training for ICPC?

What to do?

Before the plag check, I remember having rating of 1584 after the global round. Now it's 1575 and it got reduced by 9 points. Is it normal?