#include "race.h"
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ii pair<ll,ll>
const ll maxn=2e5+5;
const ll inf=1e15;
const ll mod=1e9+7;
ll ans=inf;
vector<ii> adj[maxn];
ll n,k;
map<ll,ll> maps[maxn];
pair<ll,ll> solve(ll n, ll p){
maps[n].insert({0,0});
ll off=0;
ll off2=0;
ll b,c;
for (auto u:adj[n]){
if (u.first==p) continue;
tie(b,c)=solve(u.first,n);
b+=u.second;
c++;
map<ll,ll> &a=maps[u.first];
if (maps[n].size()<a.size()) swap(maps[n],a),swap(off,b),swap(off2,c);
for (auto v:a){
auto it=maps[n].find(k-v.first-b-off);
if (it!=maps[n].end()){
ans=min(ans,it->second+v.second+off2+c);
}
}
for (auto v:a){
if (maps[n].find(v.first+b-off)==maps[n].end()){
maps[n][v.first+b-off]=v.second+c-off2;
} else{
maps[n][v.first+b-off]=min(maps[n][v.first+b-off],v.second+c-off2);
}
}
}
return {off,off2};
}
int best_path(int N, int K, int H[][2], int L[])
{
n=N,k=K;
for (int i=0;i<n-1;i++){
adj[H[i][0]].emplace_back(H[i][1],L[i]);
adj[H[i][1]].emplace_back(H[i][0],L[i]);
}
solve(0,-1);
return (ans==inf?-1:ans);
}
