B'This is an interactive problem. After getting AC after 13 Time Limit Exceeded verdicts on a geometry problem, Kuroni went to an Italian restaurant to celebrate this holy achievement. Unfortunately, the excess sauce disoriented him, and he 's now lost! The United States of America can be modeled as a tree (why though) with n vertices. The tree is rooted at vertex r , wherein lies Kuroni 's hotel. Kuroni has a phone app designed to help him in such emergency cases. To use the app, he has to input two vertices u and v , and it 'll return a vertex w , which is the lowest common ancestor of those two vertices. However, since the phone 's battery has been almost drained out from live-streaming Kuroni 's celebration party, he could only use the app at most lfloor frac{n}{2} rfloor times. After that, the phone would die and there will be nothing left to help our dear friend! :( As the night is cold and dark, Kuroni needs to get back, so that he can reunite with his comfy bed and pillow(s). Can you help him figure out his hotel 's location? The interaction starts with reading a single integer n ( 2 <= n <= 1000 ), the number of vertices of the tree. Then you will read n-1 lines, the i -th of them has two integers x_i and y_i ( 1 <= x_i, y_i <= n , x_i ne y_i ), denoting there is an edge connecting vertices x_i and y_i . It is guaranteed that the edges will form a tree. Then you can make queries of type "? u v" ( 1 <= u, v <= n ) to find the lowest common ancestor of vertex u and v . After the query, read the result w as an integer. In case your query is invalid or you asked more than lfloor frac{n}{2} rfloor queries, the program will print -1 and will finish interaction. You will receive a Wrong answer verdict. Make sure to exit immediately to avoid getting other verdicts. When you find out the vertex r , print "! r " and quit afte'...