#include <bits/stdc++.h>
using namespace std;
#define sz(v) ((int)((v).size()))
#define all(v) (v).begin(), (v).end()
#define pb push_back
#define coord_comp(v) sort(all(v)), v.erase(unique(all(v)), v.end())
#define v_index(v, x) (lower_bound(all(v),x)-(v).begin())
typedef pair<int,int> pp;
typedef long long ll;
#include "race.h"
int n,k;
vector<pp> edge[200001];
bool dead[200010];
int nt;
int pre_time[200010];
int pre_par [200010];
int pre_size[200010];
int pre_mcsz[200010];
void pre_dfs(int x){
pre_size[x]=1;
pre_mcsz[x]=0;
pre_time[x]=nt;
for(pp ep : edge[x]){
int y = ep.first;
if(dead[y] || (pre_time[y]==nt && pre_par[x]==y)) continue;
pre_par[y]=x;
pre_dfs(y);
pre_mcsz[x] = max(pre_mcsz[x], pre_size[y]);
pre_size[x] += pre_size[y];
}
}
int find_cent(int root){
++nt;
pre_par[root] = -1;
pre_dfs(root);
int sz=pre_size[root];
while(true){
if(pre_mcsz[root] <= sz/2) break;
for(pp ep:edge[root]){
int y=ep.first;
if(dead[y] || pre_par[root]==y) continue;
if(pre_mcsz[root] == pre_size[y]){
root=y; break;
}
}
}
return root;
}
int ans=2e9;
int par[200010];
void dfs_child(int x, int depth, int dc, set<pp>& s){
s.insert({depth,dc});
for(pp ep:edge[x]){
int y=ep.first;
if(dead[y] || par[x]==y) continue;
par[y]=x;
dfs_child(y, depth+ep.second, dc+1, s);
}
}
inline void find_pairs(pp& t,multiset<pp>& s){
if(t.first > k) return;
auto it=s.lower_bound({k-t.first,0});
if(it!=s.end() && it -> first == k-t.first){
ans = min(ans, t.second + it->second);
}
}
void treat_root(int x){
vector<set<pp>> sets;
for(pp ep:edge[x]){
int y=ep.first;
if(dead[y]) continue;
par[y]=x;
set<pp> ns;
dfs_child(y, ep.second, 1, ns);
sets.pb(ns);
}
multiset<pp> s;
for(auto& ss:sets){
for(pp t:ss) s.insert(t);
}
s.insert({0,0});
for(auto& v:sets){
for(auto t:v) s.erase(s.find(t));
for(auto t:v) find_pairs(t, s);
for(auto t:v) s.insert(t);
}
}
int best_path(int N, int K, int H[][2], int L[]){
n=N; k=K;
for(int i=0; i<n-1; ++i){
edge[H[i][0]].emplace_back(H[i][1], L[i]);
edge[H[i][1]].emplace_back(H[i][0], L[i]);
}
queue<int> q;
q.push(1);
while(q.size()){
int t = q.front(); q.pop();
int cent = find_cent(t);
treat_root(cent);
dead[cent] = true;
for(pp ep:edge[cent]){
int y = ep.first;
if(!dead[y]){
q.push(y);
}
}
}
if(ans == int(2e9)) ans=-1;
return ans;
}
