#include <bits/stdc++.h>
using namespace std;
#define f first
#define s second
int K, ans = INT_MAX; vector<pair<int, int>> adj[200005]; set<pair<int, int>> S[200005];
void dfs(int i, int p, int dis, int dep){
S[i].insert({dis, dep});
for (auto nxt : adj[i]) if (nxt.f != p){
dfs(nxt.f, i, dis+nxt.s, dep+1);
if (S[i].size() < S[nxt.f].size()) swap(S[i], S[nxt.f]);
for (auto d : S[nxt.f]){
int other = K+2*dis-d.f; auto x = S[i].lower_bound({other, -1});
if (x != S[i].end() and (*x).f == other) ans = min(ans, d.s+(*x).s-2*dep);
}for (auto d : S[nxt.f]) S[i].insert(d);
}
}
int best_path(int n, int k, int h[][2], int l[]){
for (int i = 0; i < n-1; i++){
adj[h[i][0]].push_back({h[i][1], l[i]});
adj[h[i][1]].push_back({h[i][0], l[i]});
}K = k; dfs(0, 0, 0, 0); return (ans == INT_MAX) ? -1 : ans;
}
