#include "race.h"
#include<bits/stdc++.h>
using namespace std;
const int N=200005;
int sz[N], e[N], z1[N], z2[N], o, k, K, Ans=N;
vector <pair<int, int> > v[N];
map<int, int> m[N];
void solve(int x=0, int pa=0){
sz[x]=1;
int mx=0, Y, D;
for (auto [y,d]:v[x]){
if(y==pa)continue;
solve(y, x);
sz[x]+=sz[y];
if(sz[y]>mx) mx=sz[y], Y=y, D=d;
}
if(sz[x]==1) e[x]=o++;
else z1[x]=z1[Y]+D, z2[x]=z2[Y]+1, e[x]=e[Y];
m[e[x]][0-z1[x]]=0-z2[x];
for (auto [y,d]:v[x]){
if(y==pa||y==Y)continue;
for(auto [kk,ans]:m[e[y]]){
k=kk+d+z1[y]+z1[x];
ans+=1+z2[y]+z2[x];
if(m[e[x]].find(K-k)!=m[e[x]].end()) Ans=min(Ans, ans+m[e[x]][K-k]);
}
for(auto [kk,ans]:m[e[y]]){
k=kk+d+z1[y]-z1[x];
ans+=1+z2[y]-z2[x];
if(m[e[x]].find(k)==m[e[x]].end() || m[e[x]][k]>ans) m[e[x]][k]=ans;
}
}
if(m[e[x]].find(K-z1[x])!=m[e[x]].end())Ans=min(Ans,z2[x]+m[e[x]][K-z1[x]]);
}
int best_path(int n, int k, int H[][2], int L[]){
K=k;
for (int i=0; i<n-1; i++)
v[H[i][0]].push_back({H[i][1],L[i]}),
v[H[i][1]].push_back({H[i][0],L[i]});
solve();
return (Ans==N)?-1:Ans;
}
