UPD: Thanks to jalsol and purplesyringa for solution to this problem. And yes, it was my problem, not GCC's one) Moreover, it was because #pragma GCC optimize("Ofast") and it's not a big question why it doesn't work in Clang :)

As you may know, usually on competitions (especially when you're coding on linux OS) GCC compiler is being used. And GCC is utterly the most popular one, I can't argue on this point. What about Clang — it's commonly known as MacOS compiler because Apple with zealous gruffness built it in the all of their PC products.

So a few weeks ago I switched OS from Ubuntu to Deepin because according to some circumstances I thought that my OS had been crashing) and btw I was right and btw Deepin is much user friendly than Ubuntu. So I changed OS then installed Clion and closed my PC, and for a week or so I used only my mac laptop, because it was just improbable to debug in such a fword compiler. Like ok, you open an application (CodeBlocks or Clion) begin debugging and by example you want to look at the variable that as you thought has some useful information that may help you rectify the thing. But instead of your variable you get "< optimized_out >" and you're obliged to make this variable global and it makes you waste some time). Ok this is not the whole problem, when you're trying :) to debug some passage of the code instead of looking through all lines of it (step by step) as Clang compiler does, you're striding, making giant leaps on other uproar compiler is kinda goading you, and in this hustle is easy to forget what you have been doing)))

Clang does NOT have this all stuff, maybe it's not the best in compiling :) or running program, but it's marvelous in debugging. So if you're interested in using a debugger, move to Clang. Good luck on contest. Bye!

Evidences:

First

GCC

Clang

Second

GCC

Clang