To all saying "Ugh no time!" At this point, there are still 7 and a half hours remaining. You can easily qualify (20 points) in under an hour.<p>That being said, #4 is the only one that tripped me up - I'm think the solution is very simple and elegant but all I can think in my head is something along the lines of ray-tracing. Back to the drawing board!
Problem D (the only nontrivial problem) was actually in an ICPC regional a few years ago (south american perhaps?) so a lot of people will have seen this one before.