#include <bits/stdc++.h>
#include "race.h"
using namespace std;
typedef long long ll;
const int N=200000;
const int K=1000000;
vector<array<int,2>> v[N];
int root=-1;
int sz[N];
int c[N][18];
ll d[N][18];
int lvl[N];
bool vis[N];
vector<int> ch[N];
vector<int> st[N];
int best[K+1];
int res=N;
int k;
void chmin(int &a,int b){a=min(a,b);}
void find_sz(int a,int p)
{
sz[a]=1;
for(auto [to,l]:v[a])
{
if(to==p||vis[to]) continue;
find_sz(to,a);
sz[a]+=sz[to];
}
}
int find_centroid(int a,int p,int n)
{
for(auto [to,l]:v[a]) if(to!=p&&!vis[to]&&sz[to]>n/2) return find_centroid(to,a,n);
return a;
}
void find_d(int a,int p,int level)
{
for(auto [to,l]:v[a])
{
if(to==p||vis[to]) continue;
c[to][level]=c[a][level]+1;
d[to][level]=d[a][level]+l;
find_d(to,a,level);
}
}
void build_cd(int a,int p)
{
find_sz(a,-1);
int centroid=find_centroid(a,-1,sz[a]);
lvl[centroid]=(p!=-1?lvl[p]+1:0);
if(p!=-1) ch[p].push_back(centroid);
else root=centroid;
find_d(centroid,-1,lvl[centroid]);
vis[centroid]=1;
for(auto [to,l]:v[centroid]) if(!vis[to]) build_cd(to,centroid);
}
void go(int a)
{
st[a].push_back(a);
for(int b:ch[a])
{
go(b);
for(int to:st[b]) st[a].push_back(to);
}
int l=lvl[a];
best[0]=0;
for(int b:ch[a])
{
for(int to:st[b]) if(d[to][l]<=k&&best[k-d[to][l]]!=-1) chmin(res,c[to][l]+best[k-d[to][l]]);
for(int to:st[b]) if(d[to][l]<=k&&(best[d[to][l]]==-1||c[to][l]<best[d[to][l]])) best[d[to][l]]=c[to][l];
}
for(int x:st[a]) if(d[x][l]<=k) best[d[x][l]]=-1;
}
int best_path(int n,int tk,int h[][2],int l[])
{
for(int i=0;i<n-1;i++)
{
int a=h[i][0],b=h[i][1],w=l[i];
v[a].push_back({b,w});
v[b].push_back({a,w});
}
k=tk;
build_cd(0,-1);
memset(best,255,sizeof(best));
go(root);
if(res==N) res=-1;
return res;
}
