#include "race.h"
#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define ff first
#define ss second
#define in insert
const int mxn=2e5+10;
vector<pair<int,int> > g[mxn];
int ans=-1,n,k,vis[mxn],sub[mxn];
int cn[1000000];
void dfs(int to,int fr)
{
sub[to]=1;
for(auto &x : g[to])
{
if(x.ff==fr || vis[x.ff]) continue;
dfs(x.ff,to);
sub[to]+=sub[x.ff];
}
}
int get_cen(int to,int fr,int sz)
{
for(auto &x : g[to])
{
if(x.ff==fr || vis[x.ff]) continue;
if(sub[x.ff]>sz/2) return get_cen(x.ff,to,sz);
}
return to;
}
void up(int tmp,int cnt)
{
if(tmp==k)
{
if(ans==-1) ans=cnt;
else ans=min(ans,cnt);
}
else
{
if(cn[k-tmp])
{
if(ans==-1) ans=cnt+cn[k-tmp];
else ans=min(ans,cnt+cn[k-tmp]);
}
}
}
void dfs2(int to,int fr,int tmp,int cnt)
{
if(tmp>k) return;
up(tmp,cnt);
for(auto &x : g[to])
{
if(x.ff==fr || vis[x.ff]) continue;
dfs2(x.ff,to,tmp+x.ss,cnt+1);
}
}
void upd(int to,int fr,int tmp,int cnt)
{
if(tmp>=k) return;
cn[k-tmp]=(cn[k-tmp]==0 ? cnt : min(cn[k-tmp],cnt));
for(auto x : g[to])
{
if(x.ff==fr || vis[x.ff]) continue;
upd(x.ff,to,tmp+x.ss,cnt+1);
}
}
void solve(int id)
{
dfs(id,-1);
id=get_cen(id,-1,sub[id]);
for(auto &x : g[id])
{
if(vis[x.ff]) continue;
dfs2(x.ff,id,x.ss,1);
upd(x.ff,id,x.ss,1);
}
vis[id]=1;
memset(cn,0,sizeof(cn));
for(auto &x : g[id])
{
if(vis[x.ff]) continue;
solve(x.ff);
}
}
int best_path(int N, int K, int h[][2], int l[])
{
n=N;
k=K;
memset(vis,0,sizeof(vis));
for(int i=0; i<N-1; i++)
{
g[h[i][0]].pb({h[i][1],l[i]});
g[h[i][1]].pb({h[i][0],l[i]});
}
solve(0);
return ans;
}
