#include "race.h"
/*
* Author : shora
*/
#include <bits/stdc++.h>
#define print(_v) for (auto &_ : _v) {cerr << _ << ' ';} cerr << endl;
using namespace std;
using ll = long long;
const int oo = 1e9;
const int N = 5e5;
struct C {
int v, w;
C(int v, int w): v(v), w(w) {}
};
vector<C> G[N];
int dep[N];
int n, k;
int res = oo;
void dfs(int u, int e = -1, int dis = 0) {
if (k < dis)
return;
if (e != -1)
dep[u] = dep[e] + 1;
else
dep[u] = 0;
if (dis == k)
res = min(res, dep[u]);
for (C& c : G[u]) if (c.v != e) {
dfs(c.v, u, dis + c.w);
}
}
int best_path(int n, int K, int H[][2], int L[]) {
k = K;
for (int i = 0, u, v, w; i < n-1; ++i) {
u = H[i][0]; v = H[i][1]; w = L[i];
G[u].push_back(C(v, w));
G[v].push_back(C(u, w));
}
for (int i = 0; i < n; ++i)
dfs(i);
return res == oo ? -1 : res;
}
