open System open System.Collections.Generic [] module Cin = let read f = stdin.ReadLine() |> f let reada f = stdin.ReadLine().Split() |> Array.map f let readChars() = read string |> Seq.toArray let readInts() = readChars() |> Array.map (fun x -> Convert.ToInt32(x.ToString())) [] module Cout = let writer = new IO.StreamWriter(new IO.BufferedStream(Console.OpenStandardOutput())) let print (s: string) = writer.Write s let println (s: string) = writer.WriteLine s let inline puts (s: ^a) = string s |> println type UnionFind = { /// 添字iが属するグループID par: int array /// 各集合の要素数 size: int array } [] [] module UnionFind = /// O(n) let init (n: int): UnionFind = let par = Array.init n id let size = Array.init n (fun _ -> 1) { UnionFind.par = par size = size } /// x: 0-indexed let rec root (x: int) (uf: UnionFind): int = let par = uf.par match x = par.[x] with | true -> x | false -> let px = par.[x] par.[x] <- root px uf par.[x] /// 連結判定 let find (x: int) (y: int) (uf: UnionFind) = (root x uf) = (root y uf) let unite (x: int) (y: int) (uf: UnionFind): bool = let par, size = uf.par, uf.size let rx, ry = root x uf, root y uf match rx = ry with | true -> false | _ -> // マージテク(大きい方に小さい方を併合) let large, small = if size.[rx] < size.[ry] then ry, rx else rx, ry par.[small] <- large size.[large] <- size.[large] + size.[small] size.[small] <- 0 true /// 素集合のサイズ /// x: 0-indexed let size (x: int) (uf: UnionFind): int = let rx = root x uf uf.size.[rx] /// 連結成分の個数 /// O(n) let treeNum (uf: UnionFind): int = let par = uf.par let mutable cnt = 0 par |> Array.iteri (fun i x -> if i = x then cnt <- cnt + 1) cnt let main() = let n = read int let uf = UnionFind.init n let degs = Array.zeroCreate n for i in 0 .. n - 2 do let [| u; v |] = reada int UnionFind.unite u v uf |> ignore degs.[u] <- degs.[u] + 1 degs.[v] <- degs.[v] + 1 let num = uf |> UnionFind.treeNum let A = "Alice" let B = "Bob" if num >= 3 then A elif num = 2 then let ok = degs |> Array.tryFind (fun x -> x < 2) match ok with | Some _ -> A | _ -> B else B |> puts () main() writer.Close()