I've implemented an octtree (I used http://www.nist.gov/dads/HTML/octree.html as a reference on this data structure, it's easy to understand. Just try it!)

I've got AC, but I cann't make it run quicker, than 0.4 sec. If you need my source code to help me, or have anything else to tell me, feel free to e-mail to urrel AT rambler DOT ru.

Well, there has been a way to optimize the logic of my algo, that wasn't evident for me at first... Here is the result (0.109 sec):

http://acm.timus.ru/rating.aspx?space=1&num=1331
http://acm.timus.ru/status.aspx?space=1&pos=1004143

Happy New Year to everybody (Right now it is 31 dec 2004, 22:45 here, is Astrakhan). Be happy, Don't worry!

Good luck in solving problems,
  Rafail Ahmadisheff.