Even if you are not a registered contestant at BOI 2021, you can take the challenge and participate in the online mirror contests that BOI 2021 is offering. They will be run shortly after the official contests:
- April 24, 2021, 14:00-19:00 UTC: Mirror of BOI 2021, Day 1
- April 25, 2021, 14:00-19:00 UTC: Mirror of BOI 2021, Day 2
This is the contest server for the BOI 2021 online mirror: opencontest.boi2021.uni-luebeck.de
You need to register there, before participating. At this time, you can register for day 1 only, but the credentials will remain valid on day 2.