Isn't it weird that ColdSu made correct submissions for problems B and C within a window of less than a minute? And he solved both this problems so fast that by the time he finished them, he was leading the contest, being ahead of many top-tier coders, like Um_nik, natsugiri and dreamoon_love_AA.

So, is there any reasonable explanation for this that doesn't involve cheating? I can't think of any plausible one.