Doing that won't ensure that you chose i <= j <= k when building sum a[i] * p + a[j] * q + a[k] * r. One of the right solutions (I don't know if there are more) is egor.okhterov's above.

When will registration be closed?

Hmm I solved all kinds of problems, especially from my national contests... And, I participated in every online contest, it helps a lot! Also, after the contest ends I try to solve the problems I couldn't solve during the contest, hope that helps.

Yeah, well, I had a great teacher during that time :).

Nice problems, I loved them! (although my D failed on test 78 :( ). Still, more than the problems, I love that you put a list with the winners, which is very nice :). (at my previous div2 I was first and that guy didn't put a list with the winners, I will put him in my "black list" hehehe....)

Why no congratulations on the winners like in other rounds? :(