Shortly speaking it is one of the most respected annual celebrations in Islam (like Easter for us, for example).

However celebration is linked with very ancient story — the temptation of Abraham — the grandfather of Israel (who is himself the father of 12 founders of 12 Tribes of Israel) by God (God was asking to sacrifice Abraham's only son, Ismail — though saved him at last moment). Muslims call this decent man Ibrahim and respect them as one of the first founders of monotheistic religion.

So you see, this is one of those celebration which links somehow followers of Islam and Christianity.

You know that there are many contestants (and even contest authors) from Tajikistan, Kazakhstan, Iran etc. so let us join this congratulation warmly!

(Heh, you see — sometimes politics separate people — but Codeforces join them again — I think it is cool)

Wiki: Abraham, Jacob/Israel, Kurban-Bayram/Eid al-Adha