#include "race.h"
#include<bits/stdc++.h>
using namespace std;
#define pb push_back
int n,ans=1e9,k,tam[200005],vis[200005],min_longi[1000005];
vector<pair<int,int> > v[200005];
void tamanio_tree(int u,int p){
tam[u]=1;
for(auto [node,w]:v[u]){
if(vis[node]==0 && node!=p){
tamanio_tree(node,u);
tam[u]+=tam[node];
}
}
}
int centroid_descomposition(int u,int p,int want){
for(auto [node,w]:v[u]){
if(node!=p && vis[node]==0){
if(tam[node]>want)return centroid_descomposition(node,u,want);
}
}
return u;
}
void dfs(int u,int p,int type,int depth,int lv){
if(depth>k)return;
if(type==1){
ans=min(ans,lv+min_longi[k-depth]);
}else if(type==0){
min_longi[depth]=min(min_longi[depth],lv);
}else{
min_longi[depth]=1e9,min_longi[k-depth]=1e9;
}
for(auto [node,w]:v[u]){
if(node!=p && vis[node]==0){
dfs(node,u,type,depth+w,lv+1);
}
}
}
void all_trees(int u){
tamanio_tree(u,u);
int cen=centroid_descomposition(u,u,tam[u]/2);
vis[cen]=1;
for(auto [node,w]:v[cen]){
if(vis[node]==0){
dfs(node,node,2,w,1);
}
}
min_longi[0]=0;
for(auto [node,w]:v[cen]){
if(vis[node]==0){
dfs(node,node,1,w,1);
dfs(node,node,0,w,1);
}
}
for(auto [node,w]:v[cen]){
if(vis[node]==0){
all_trees(node);
}
}
}
int best_path(int N, int K, int H[][2], int L[]){
n=N,k=K;
for(int i=0;i<n-1;i++){
v[H[i][0]+1].pb({H[i][1]+1,L[i]});
v[H[i][1]+1].pb({H[i][0]+1,L[i]});
}
for(int i=1;i<=n;i++){
vis[i]=0;
}
for(int i=1;i<=1000000;i++){
min_longi[i]=1e9;
}
all_trees(1);
return (ans == 1e9) ? -1 : ans;
}
