#include <bits/stdc++.h>
#include "race.h"
using namespace std;
typedef long long ll;
#define f(i,a,b) for(int i = a; i < b; i++)
#define ff first
#define ss second
const ll N = 1e6 + 5;
ll n, k, sz[N], ans = N, dist[N], dreal[N], aux[N];
bool on[N];
vector <pair<int,ll>> adj[N];
vector <int> ra;
int size(int u, int f){
sz[u] = 1;
for(auto v: adj[u]) if(v.first != f and !on[v.first]) sz[u] += size(v.first, u);
return sz[u];
}
int get_centroid(int u, int f, int curr_size){
for(auto v: adj[u]) if(v.first != f and !on[v.first] and sz[v.first]*2 > curr_size) return get_centroid(v.first, u, curr_size);
return u;
}
void get_tree(int u, int f){
ra.push_back(u);
for(auto v: adj[u]) if(v.first != f and !on[v.first]) get_tree(v.first, u);
}
void dfs(int u, int f){
for(auto p: adj[u]){
ll v = p.first, w = p.second;
if(v == f or on[v]) continue;
dist[v] = dist[u] + 1;
dreal[v] = dreal[u] + w;
dfs(v, u);
}
}
void solve(int u, int f){
int cen = get_centroid(u, f, size(u, f));
on[cen] = 1, dist[cen] = dreal[cen] = 0;
dfs(cen, f);
vector <ll> AUX;
for(auto p: adj[cen]){
int v = p.ff;
if(v == f or on[v]) continue;
ra.clear(); get_tree(v, cen);
for(int x: ra){
if(dreal[x] == k){
ans = min(ans, dist[x]);
}
else if(dreal[x] > k) continue;
ans = min(ans, aux[k-dreal[x]] + dist[x]);
}
for(int x: ra){
if(dreal[x] >= k) continue;
aux[dreal[x]] = min(aux[dreal[x]], dist[x]);
AUX.push_back(dreal[x]);
}
}
for(int x: AUX) aux[x] = N;
for(auto v: adj[cen]) if(v.first != f and !on[v.first]) solve(v.first, cen);
}
int best_path(int m, int K, int H[][2], int L[]){
n = m, k = K;
f(i,0,n-1){
ll u = H[i][0], v = H[i][1], w = L[i];
adj[u].push_back({v, w});
adj[v].push_back({u, w});
}
f(i,0,N) aux[i] = N;
solve(0, -1);
if(ans == N) ans = -1;
return ans;
}
