In the last round, I noticed something interesting: only a relatively small number of people solved F1, even though the solution itself felt much easier than you would expect from an F problem.

Just from the title and its position in the contest, the problem looks intimidating — XOR, transformations, and on top of that, it is labeled F. Because of that, I think many people may have skipped it or assumed it would be too hard.

But after making a few observations, the solution becomes quite straightforward. There is no really heavy data structure or advanced math involved — the main thing is to understand what is actually happening after each transformation.

To me, this is a good example of a problem where the letter scared people more than the actual difficulty :)

I wonder why so few people solved it during the round: was it because of time pressure, because the problem looked too scary, or because the main idea was still not that obvious?