Recently, I started solving codeforces problems from the beginning. I just solved Codeforces Beta Round #8. I couldn't find any tutorial for the round so I decided to write tutorial for the last two problems. The others I solve long time ago in the real contest. Problem E took me quite some time and I couldn't find even a discussion about it, so here are my solutions.
The main observation for this problem is the following: If Alan and/or Bob is at some point X and moves following some curve and travels distance d, then the point at which they finish can be ANY point on or inside the circle with center X and radius d. In other words: If you start at some point X and go to some point Y, you can do this on as long curve as we want(only not shorter then the