Welcom! Glad it played out well.

Hello @yuryk, @JohanWilthnik and @Bling4Basics!
Many thanks to all of you for your time dedicated for helping me!
I have found the reason of my problem - it is bug in my code.
Sorry for taking your time - i should have been more attentive being solving this problem myself.
And thanks again to all!

Yuri, thank you for your suggestions. You were completely right. There are bug in my solution which causes infinite loop on particular tests. Discovering this fact took so much time just because i had used console printing not thoroughly enough for the first time:-)

Sorry, Yuri, but someone has desided that your comment contains spoiler, and i hasn't read it :-(
I smell a conspiracy here :-)

Hello, Yuri!
Could it be possible, that for final qualification (attemt) somehow server dedicates less resources than for sample tests running?
I just can't find reasonal explanation to the fact, that my code easily passes same set of tests as on final qualification but only in "sample tests" environment...

It's most propably server problem.
At this moment i can't even run sample tests:

Server Execution Error:

The server timed out waiting for the request to be processed. This may be due to high server load. Please try your request again.

So for now it's just getting worse...

Update: "RUN SAMPLE TEST" works again:

Time: 1884ms Passed: 8 Failed: 0

Test Results:
BasicTests
ShouldPassAllTests
Test_0_Medium
Test_1_Hard
Test_2_Hard
Test_3_VeryHard
Test_4_VeryHard
Test_5_VeryHard
Test_6_VeryHard
You have passed all of the tests! :)

But "ATTEMPT" still gives me:
"Process was terminated. It took longer than 12000ms to complete "

Yury did the C# version.

Yury, or anybody else who does C#, can you confirm or deny this problem?

We have a different C# complaint.

Could you see if his problem is reproducible? It might also be a platform issue, I have no way to tell.

I'm on it. But I don't know when I'll finish...

My bad! It is C# !
Gone even further - placed all 8 tests from attempt, and its solutions in Sample Tests.
Pressing "RUN SAMPLE TEST". Al tests succesfully passed. Completion time floats around 1900ms like "Time: 1883ms Passed: 8 Failed: 0."
But pressing "ATTEMPT" gives me same issue as described above.
Seeing such behavior for couple of days, maybe more.

Or tell us in which language you are having this problem, and we could see if we can replicate the problem.

But help us help you; tell us what language!

might be a server problem. Try again in a few hours, maybe.

There are some strange behavior while trying to attempt solution.
Output log shows stops on reason "Process was terminated. It took longer than 12000ms to complete" after 7 test out of 8 being completed.
Sum of completion time for first passed 7 tests is about 1200ms.
I've snatched test cases by printing arguments and run it on my machine. All 8 tests vere completed in approx 1600ms.
Then i've added last test case and its solution to the sample tests. Completion time of added test is 37ms.
Doing some heavy math: 1200+37=1237ms running on codewars servers. It is even faster than on my own PC and far below 12000ms!
So can anyone tell me what i am doing wrong, please?
Beg your pardon for my English - it's not my native.