Today I screencast and explained solutions of problems A–D and F. The video is uploaded to YouTube: https://youtu.be/B48ykX0NpUY

I have to inform that the round quality wasn't exceptionally high: the translation was noticeably Google translated from Russian (for example, представление has at least two meanings — representation or performance, and Google Translate wasn't able to discriminate between these two), the pretests were weak in B, C and F (many people were simply TL-hacked or had their solution fail during system testing). I will elaborate on problem F: there I wrote a square root decomposition with incorrect constants, but still got AC though my solution was incorrect on these simple tests:

2 3
2 2

and

4 24
5 5 5 5

Nevertheless I knew what to expect (I call such rounds contests for schoolchildren) and overall experience was satisfactory.