#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include "race.h"
using namespace std;
#define INF 1145141919
#define rep(i, n) for (int i=0; i<(n); i++)
#define _1 first
#define _2 second
#define all(x) x.begin(), x.end()
#define pb push_back
typedef pair<int, int> P;
inline void chmin(int &x, int v) { if (x > v) x = v; }
int N, K;
int ans;
vector<P> G[200000];
void dfs(int x, int p, int r, int d) {
if (d == K) ans = min(ans, r);
for (P pp : G[x]) {
int t = pp._1, nd = min(d+pp._2, INF);
if (t == p) continue;
dfs(t, x, r+1, nd);
}
}
int dp[200000][101][2];
int src[200000][101];
void update(int x, int k, int v, int s) {
if (v < dp[x][k][0]) {
dp[x][k][1] = dp[x][k][0];
dp[x][k][0] = v;
src[x][k] = s;
}
else if (v < dp[x][k][1]) dp[x][k][1] = v;
}
int get(int x, int k, int s) {
int e = 0;
if (src[x][k] == s) e = 1;
return dp[x][k][e];
}
void dfs2(int x, int p) {
update(x, 0, 0, -1);
for (P pp : G[x]) {
int t = pp._1, l = pp._2;
if (t == p) continue;
dfs2(t, x);
for (int k=0; k<=K-l; k++) update(x, k+l, dp[t][k][0]+1, t);
}
}
void dfs3(int x, int p, int pd) {
if (p != -1) {
for (int k=0; k<=K-pd; k++) update(x, k+pd, get(p, k, x)+1, p);
}
for (P pp : G[x]) {
int t = pp._1, l = pp._2;
if (t == p) continue;
dfs3(t, x, l);
}
}
int best_path(int n, int k, int H[][2], int L[]) {
N = n, K = k;
rep(i, N) G[i].clear();
rep(i, N-1) {
G[H[i][0]].pb(P(H[i][1], L[i]));
G[H[i][1]].pb(P(H[i][0], L[i]));
}
ans = INF;
if (K <= 100) {
// subtask 3
rep(i, N) rep(j, K+1) dp[i][j][0] = dp[i][j][1] = INF, src[i][j] = -1;
dfs2(0, -1);
dfs3(0, -1, -1);
rep(i, N) ans = min(ans, dp[i][K][0]);
}
else {
// subtask 1&2
rep(i, N) dfs(i, -1, 0, 0);
}
if (ans == INF) ans = -1;
return ans;
}
