In some Codeforces problems (for example, problem 545C), you may notice two different interval notations, such as:

[a, b] and [a; b]

This can be confusing at first, but there is actually no difference in meaning.

In many Russian mathematical texts, the semicolon ; is used as the separator in intervals, while in most European and English texts, the comma , is used instead. Since many Codeforces problems are translated from Russian, both notations can appear.