#include"race.h"
#include<bits/stdc++.h>
#ifdef IOI2021SG
#include"grader.cpp"
#endif
using namespace std;
#define fr first
#define sc second
vector<pair<int,int>>g[200005];
const int INF=2e9;
int k,ans=INF;
int sz[200005];
bool vis[200005];
pair<int,int>mt[1000005];
int timer;
void calc_sz(int v,int p){
sz[v]=1;
for(auto to:g[v])if(to.fr!=p&&!vis[to.fr]){
calc_sz(to.fr,v);
sz[v]+=sz[to.fr];
}
}
int centroid(int v,int p,int num){
for(auto to:g[v])if(to.fr!=p&&!vis[to.fr])
if(sz[to.fr]>num)return centroid(to.fr,v,num);
return v;
}
void go(int v,int p,int depth,int weight){
if(weight>k)return;
if(mt[k-weight].fr==timer)
ans=min(ans,depth+mt[k-weight].sc);
for(auto to:g[v])if(to.fr!=p&&!vis[to.fr])go(to.fr,v,depth+1,weight+to.sc);
}
void update(int v,int p,int depth,int weight){
if(weight>k)return;
if(mt[weight].fr==timer)mt[weight].sc=min(mt[weight].sc,depth);
else mt[weight]={timer,depth};
for(auto to:g[v])if(to.fr!=p&&!vis[to.fr])update(to.fr,v,depth+1,weight+to.sc);
}
void decompose(int v){
calc_sz(v,v);
v=centroid(v,v,sz[v]>>1);
timer++;
mt[0]={timer,0};
for(auto to:g[v]){
if(vis[to.fr])continue;
go(to.fr,v,1,to.sc);
update(to.fr,v,1,to.sc);
}
vis[v]=true;
for(auto to:g[v])if(!vis[to.fr])decompose(to.fr);
}
int best_path(int n,int K,int h[][2],int l[]){
k=K;
for(int i=1;i^n;i++){
g[h[i-1][1]].push_back({h[i-1][0],l[i-1]});
g[h[i-1][0]].push_back({h[i-1][1],l[i-1]});
}
decompose(0);
if(ans==INF)return -1;
return ans;
}
/*
3 3
0 1 1
1 2 1
-1
4 3
0 1 1
1 2 2
1 3 4
2
11 12
0 1 3
0 2 4
2 3 5
3 4 4
4 5 6
0 6 3
6 7 2
6 8 5
8 9 6
8 10 7
2
*/
