Hello! I hope all of you enjoyed my contest!

Behind story of A:

• I tried to make the easiest Div2A ever. Will it work? :)

Behind story of B:

• I tried to block various heuristics. There were some critical heuristics which could pass so many cases. Fortunately I blocked them during testing period, so I hope there won't be much FST this time.

Behind story of D2C/D1A:

• Originally, there was a different problem for this position. But it used XOR. As I made new D2E/D1C problem, I threw old D2C/D1A away and put this.

Behind story of D2D/D1B:

• This problem is the most popular problem among testers. I also like this problem a lot.

Behind story of D2E/D1C:

• Feedback for this problem was too different by testers.
• I made this problem by modifying Number Discovery, which is one of my previous problems.
• If you OEIS this, then you may find you can use Nimber Arithmetic to solve this.

Behind story of D1D:

• This problem was supposed to be D2E at first. But all LGM testers failed this problem during VC, so we thought that this problem's difficulty is high. Meanwhile, I found that old D1D problem can be easily googled, so we removed that problem, push this problem to be D1D, and made another D1C problem. I will share old D1D later.

Behind story of D1E:

• Thanks tzuyu_chou for writing this problem. She is genius in both singing and problemsolving.