B"The city of F. can be represented as a tree. A famous fugitive is hiding in it, and today a faithful police officer decided to catch him at all costs. The police officer is stronger than the fugitive, but the fugitive is much faster than the former. That is why the pursuit proceeds as follows. At the moment t = 0 the police officer appears at the vertex with number s , and the fugitive spawns at any other vertex of his choice. After that, they take turns, starting with the police officer. Note that the fugitive managed to attach a radio bug to the police officer's badge a week ago, so the fugitive knows the location of the police officer at every moment (in particular, he knows the number s ). On the contrary, the police officer knows nothing about the fugitive's movements and will only be able to detect him at the very moment she catches him. The police officer aims to catch the fugitive as fast as possible, and the fugitive aims to be caught as late as possible. Since the chase can be thought of as a game with incomplete information, participants can use mixed (probabilistic) strategies -- thus, the police officer acts to minimize the expected duration of the chase, and the fugitive -- to maximize it. Find the mathematical expectation of the duration of the chase with optimal actions of the police officer and the fugitive. It can be proven that it is always finite. In particular, with optimal strategies, the probability that the chase continues indefinitely is equal to zero. The first line contains an integer n -- the number of vertices in the tree ( 2 <= n <= 100 ). The next n - 1 lines describe the city of F.: each of them contains a pair of integers u_i , v_i -- the numbers of the ends of an edge ( 1 <= u_i, v_i <= n ). These edges are guaranteed to form a tree. The last line contains an integer s -- the number of the vertex where the police officer initially appears ( 1 <= s <= n$"...