As we know, Codeforces has a rule regarding third-party code, which states that if you copy code from a public source available before the contest, it is not considered cheating. However, here's the issue: Codeforces first checks for code similarity between submissions. If a significant portion of the code matches across multiple accounts (typically 70% or more), Codeforces automatically flags the other submissions, except for the first one, as plagiarism.

So, what's the point of the third-party code rule?

Here is a blog related to this kind of issue, though cf didn't rejudge his solution.