#include "race.h"
#include <bits/stdc++.h>
using namespace std;
const int NN = 2e5 + 5, MM = 1e6+5;
bool used[NN];
int cnt[MM];
int len[MM];
int sz[NN];
int n, k;
vector<pair<int, int>> edges[NN];
void dfs_size(int u, int p){
sz[u] = 1;
for(auto X : edges[u]){
int v = X.first;
if(used[v] || v == p)continue;
dfs_size(v, u);
sz[u] += sz[v];
}
}
int centroid(int u, int p, int size){
for(auto X : edges[u]){
int v = X.first;
if(used[v] || v == p)continue;
if(sz[v] > size/2)return centroid(v, u, size);
}
return u;
}
vector<pair<int, int>> m;
void dfs(int u, int p, int dist, int t){
m.push_back({dist, t});
for(auto X : edges[u]){
int v = X.first;
int cost = X.second;
if(used[v] || v == p)continue;
dfs(v, u, dist+cost, t+1);
}
}
void dfs2(int u, int p, int dist, int t){
len[dist] = min(len[dist], t);
cnt[dist] ++;
for(auto X : edges[u]){
int v = X.first;
int cost = X.second;
if(used[v] || v == p)continue;
dfs2(v, u, dist+cost, t+1);
}
}
int find_min(int u){
int ans = 1e9;
for(int i=0;i<MM;i++)cnt[i] = 0, len[i] = 1e9;
dfs_size(u, u);
u = centroid(u, u, sz[u]);
cnt[0]++;
len[0] = 0;
used[u] = true;//delete centroid
for(auto X : edges[u]){
m.clear();
int v = X.first;
int cost = X.second;
if(used[v])continue;
dfs(v, u, cost, 1);
for(auto X : m){
int dist = X.first;
int time = X.second;
if(cnt[k-dist] > 0){
ans = min(ans, len[k-dist]+time);
}//cout << dist << ' ' << time << '\n';
}
for(auto X : edges[u]){
int v = X.first;
int cost = X.second;
dfs2(v, v, cost, 1);
}
}
for(auto X : edges[u]){
int v = X.first;
if(used[v])continue;
ans = min(ans, find_min(v));
}
return ans;
}
int best_path(int N, int K, int H[][2], int L[]){
n = N;
k = K;
for(int i=0;i<n-1;i++){
edges[H[i][0]].push_back({H[i][1],L[i]});
edges[H[i][1]].push_back({H[i][0],L[i]});
}
int ans = find_min(0);
// cout << '\n' << ans << '\n';
if(ans > n)ans = -1;
return ans;
}
