So, in today’s contest I had a really bad day… It started off quite well (I was the 10th person to get first problem right) and then it took me more than an hour to implement an observation I’ve made in less then 10 seconds (problem B). I gave up on C and simply sent a random solution…
Moral of the story - if you feel like you are at your peek don’t be so sure, give it an hour 
same solved A in 4 min and then took and hour for C but D is hard
after first submission, I was at 30th, after second submission I was at 61th and after third submission I was at 32th again…for the D problem I find a logic quite fast if the values of D <= 10**5, without looking at the constraints I submit it and got a wrong answer…after that I was just finding a logic for it but now capable of it and now I am waiting for the editorial because it is really an interested problem
yes
My day got worse, my “random” C solution (1-2 coloring) was actually correct and I implemented it wrongly…
yeah it was simple 1-2 coloring solution