#include <bits/stdc++.h>
#include "race.h"
using namespace std;
#define ff first
#define ss second
vector<pair<int, int> > adj[200005];
map<int, int> sum_to_dist[200005];
int sum[200005], dist[200005], N, K, ans;
void dfs(int u, int p, int s, int d){
sum_to_dist[u][s] = d;
sum[u] = s;
dist[u] = d;
for(auto v : adj[u]) if(v.ff != p) dfs(v.ff, u, s + v.ss, d + 1);
}
void merge_dfs(int u, int p){
int target = K + 2 * sum[u];
for(auto v : adj[u]){
if(v.ff == p) continue;
merge_dfs(v.ff, u);
if(sum_to_dist[v.ff].size() > sum_to_dist[u].size()) swap(sum_to_dist[v.ff], sum_to_dist[u]);
for(auto p : sum_to_dist[v.ff]) if(sum_to_dist[u].find(target - p.ff) != sum_to_dist[u].end()) ans = min(ans, sum_to_dist[u][target - p.ff] + p.ss - 2 * dist[u]);
for(auto p : sum_to_dist[v.ff]){
if(sum_to_dist[u].find(p.ff) == sum_to_dist[u].end()) sum_to_dist[u].insert(p);
else sum_to_dist[u][p.ff] = min(sum_to_dist[u][p.ff], p.ss);
}
}
}
int best_path(int n, int k, int h[][2], int l[]){
N = n; K = k;
for(int i = 0; i < n - 1; i++){
int u = h[i][0], v = h[i][1], w = l[i];
adj[u].push_back({v, w});
adj[v].push_back({u, w});
}
dfs(0, -1, 0, 0);
merge_dfs(0, -1);
return ans == INT_MAX ? -1 : ans;
}
