#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;
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 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;
rep(i, N) dfs(i, -1, 0, 0);
if (ans == INF) ans = -1;
return ans;
}
