using System; using System.IO; using System.Collections.Generic; using System.Globalization; using System.Linq; using System.Text; partial class Solver { const int mod = 1000000007; int[][] memo = new int[2001][]; int[] size = new int[2001]; int[] dfs(List> adj, int pos, int parent = -1) { int n = adj.Count; if (memo[pos] != null) return memo[pos]; int[] ret = new int[n + 1]; ret[0] = 1; size[pos] = 1; foreach (var child in adj[pos]) { if (child == parent) continue; var sub = dfs(adj, child, pos); size[pos] += size[child]; int[] next = new int[n + 1]; for (int i = 0; i <= n; i++) { if (ret[i] == 0) continue; for (int j = n - i; j >= 0; j--) { next[i + j] += (int)(1L * ret[i] * sub[j] % mod); next[i + j] %= mod; } } ret = next; } ret[size[pos]] = 1; return memo[pos] = ret; } public void Run() { int N = ni(); int K = ni(); var adj = Enumerable.Range(0, N).Select(_ => new List()).ToList(); for (int i = 0; i < N - 1; i++) { int a = ni(); int b = ni(); adj[a].Add(b); adj[b].Add(a); } var result = dfs(adj, 0); cout.WriteLine(result[K]); } } // PREWRITEN CODE BEGINS FROM HERE partial class Solver : Scanner { public static void Main(string[] args) { new Solver(Console.In, Console.Out).Run(); } TextReader cin; TextWriter cout; public Solver(TextReader reader, TextWriter writer) : base(reader) { this.cin = reader; this.cout = writer; } public Solver(string input, TextWriter writer) : this(new StringReader(input), writer) { } public int ni() { return NextInt(); } public long nl() { return NextLong(); } public string ns() { return Next(); } } public class Scanner { private TextReader Reader; private Queue TokenQueue = new Queue(); private CultureInfo ci = CultureInfo.InvariantCulture; public Scanner() : this(Console.In) { } public Scanner(TextReader reader) { this.Reader = reader; } public int NextInt() { return Int32.Parse(Next(), ci); } public long NextLong() { return Int64.Parse(Next(), ci); } public double NextDouble() { return double.Parse(Next(), ci); } public string[] NextArray(int size) { var array = new string[size]; for (int i = 0; i < size; i++) array[i] = Next(); return array; } public int[] NextIntArray(int size) { var array = new int[size]; for (int i = 0; i < size; i++) array[i] = NextInt(); return array; } public long[] NextLongArray(int size) { var array = new long[size]; for (int i = 0; i < size; i++) array[i] = NextLong(); return array; } public String Next() { if (TokenQueue.Count == 0) { if (!StockTokens()) throw new InvalidOperationException(); } return TokenQueue.Dequeue(); } public bool HasNext() { if (TokenQueue.Count > 0) return true; return StockTokens(); } private bool StockTokens() { while (true) { var line = Reader.ReadLine(); if (line == null) return false; var tokens = line.Trim().Split(" ".ToCharArray(), StringSplitOptions.RemoveEmptyEntries); if (tokens.Length == 0) continue; foreach (var token in tokens) TokenQueue.Enqueue(token); return true; } } }