#include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; typedef pair P; #define rep(i, n) for (int i=0; i<(n); i++) #define all(c) (c).begin(), (c).end() #define uniq(c) c.erase(unique(all(c)), (c).end()) #define index(xs, x) (int)(lower_bound(all(xs), x) - xs.begin()) #define _1 first #define _2 second #define pb push_back #define INF 1145141919 #define MOD 1000000007 inline void add(int &x, int v) { x += v; if (x >= MOD) x -= MOD; } int N, K; vector G[2000]; int sz[2000]; int dfs(int x, int p) { sz[x] = 1; for (int t : G[x]) { if (t == p) continue; sz[x] += dfs(t, x); } return sz[x]; } int dp[2000][2001]; int dp2[2][2001]; void f(int x, int p) { for (int t : G[x]) { if (t == p) continue; f(t, x); } int n = sz[x]; rep(i, N+1) dp2[0][i] = 0; dp2[0][0] = 1; for (int t : G[x]) { if (t == p) continue; rep(i, n+1) dp2[1][i] = 0; for (int j=n; j>=0;j--){ if (dp2[0][j] == 0) continue; rep(k, sz[t]+1) { if (j+k > n) break; add(dp2[1][j+k], (1LL*dp[t][k]*dp2[0][j])%MOD); } } swap(dp2[0], dp2[1]); } assert(dp2[0][n] == 0); dp2[0][n] = 1; rep(i, n+1) dp[x][i] = dp2[0][i]; } signed main() { ios::sync_with_stdio(false); cin.tie(0); cin >> N >> K; rep(i, N-1) { int a, b; cin >> a >> b; G[a].pb(b); G[b].pb(a); } dfs(0, -1); f(0, -1); cout << dp[0][K] << "\n"; return 0; }