#include "race.h"
#include <bits/stdc++.h>
using namespace std;
int _K, ans = 1e9, dist[1000005], dep[1000005];
vector<pair<int, int> > adj[1000005];
set<pair<int, int> > S[1000005];
void dfs(int n, int e = -1) {
S[n].emplace(dist[n], dep[n]);
for (auto u : adj[n]) {
if (u.first != e) {
dist[u.first] = dist[n] + u.second;
dep[u.first] = dep[n] + 1;
dfs(u.first, n);
if (S[n].size() < S[u.first].size()) swap(S[n], S[u.first]);
for (auto i : S[u.first]) {
auto it = S[n].lower_bound(make_pair(_K - i.first + 2 * dist[n], 0));
if (it != S[n].end() && it->first + i.first - 2 * dist[n] == _K) ans = min(ans, it->second + i.second - 2 * dep[n]);
}
for (auto i : S[u.first]) S[n].insert(i);
}
}
}
int best_path(int N, int K, int H[][2], int L[]) {
_K = K;
for (int i = 0; i < N - 1; i++) {
adj[H[i][0]].emplace_back(H[i][1], L[i]);
adj[H[i][1]].emplace_back(H[i][0], L[i]);
}
dfs(0);
return (ans == 1e9 ? -1 : ans);
}
