B"You have an integer n . Let's define following tree generation as McDic's generation: You have a tree. Determine if this tree can be made by McDic's generation. If yes, then find the parent vertex of removed vertex in tree. The first line contains integer n ( 2 <= n <= 17 ). The i -th of the next 2^{n} - 3 lines contains two integers a_{i} and b_{i} ( 1 <= a_{i} lt b_{i} <= 2^{n} - 2 ) -- meaning there is an edge between a_{i} and b_{i} . It is guaranteed that the given edges form a tree. Print two lines. In the first line, print a single integer -- the number of answers. If given tree cannot be made by McDic's generation, then print 0 . In the second line, print all possible answers in ascending order, separated by spaces. If the given tree cannot be made by McDic's generation, then don't print anything. In the first example, 3 is the only possible answer. In the second example, there are 2 possible answers. In the third example, the tree can't be generated by McDic's generation. "...