问题 H: HEX-A-GONE Trails

In each move, a player at node imust choose a neighboring node j and move to j. Remind that a player is not allowed to move to the other player's current position. After this move, node ii becomes invalid, meaning it cannot be moved to in the following moves of both players.

If a player cannot make a valid move, he will lose the game.

Please determine whether OP I has a strategy to make sure he will win.

The first line of each test case contains one integer n (1≤n≤10^5).

The second line contains two integers x,y (1≤x,y≤n, x!=y).

Each of the following n - 1lines contains two integers u,v(1≤u,v≤n, u!=v) - an edge between u,v.

It's guaranteed that ∑n≤6×10^5.