#include<bits/stdc++.h>
using namespace std;
using ll=long long;
using ar=array<ll,2>;
ll n,k,res=1e7;
vector<ar>g[200000];
ll sz[200000];
bool used[200000];
map<ll,ll>mp;
void siz(ll v, ll e){
sz[v]=1;
for(const auto&[i,w]:g[v])
if(i!=e and !used[i]) siz(i,v),sz[v]+=sz[i];
}
ll get(ll v, ll e, ll des){
for(const auto&[i,w]:g[v])
if(i!=e and !used[i] and sz[i]>des) return get(i,v,des);
return v;
}
void help(ll v, ll e, ll km, ll d, bool fill){
if(km>k) return;
if(fill){
if(!mp.count(km)) mp[km]=d;
else mp[km]=min(mp[km],d);
}
else{
if(km==k) res=min(res,d);
else if(mp.count(k-km)) res=min(res,d+mp[k-km]);
}
for(const auto&[i,w]:g[v])
if(i!=e and !used[i]) help(i,v,km+w,d+1,fill);
}
void decomp(ll v=0){
siz(v,-1);
ll c=get(v,-1,sz[v]>>1);
used[c]=1;
for(const auto&[i,w]:g[c])
if(!used[i]){
help(i,c,w,1,0);
help(i,c,w,1,1);
}
mp.clear();
for(const auto&[i,w]:g[c])
if(!used[i]) decomp(i);
}
int best_path(int N, int K, int H[][2],int L[]){
n=N;
k=K;
for(ll i=0;i<n-1;++i){
g[H[i][0]].push_back({H[i][1],L[i]});
g[H[i][1]].push_back({H[i][0],L[i]});
}
decomp();
if(res==1e7) res=-1;
return res;
}
