#include <bits/stdc++.h>
#include "race.h"
using namespace std;
using ll = long long;
#define all(x) begin(x), end(x)
#define sz(x) (int)x.size()
#define pb push_back
const int maxn = 200001;
int N, K;
vector<int> adj[maxn];
vector<pair<int, int>> adj2[maxn];
int sub[maxn];
bool done[maxn];
int subtree_size(int s, int p){
sub[s] = 1;
for(auto u: adj[s]){
if(u == p or done[u]) continue;
sub[s] += subtree_size(u, s);
}
return sub[s];
}
int get_centroid(int s, int p, int num){
for(auto u: adj[s]){
if(u == p or done[u]) continue;
if(2*sub[u] > num) return get_centroid(u, s, num);
}
return s;
}
ll ans = 1e18;
ll best[1000001];
void calc(int s, int p, bool fill, int d, int wt){
if(wt > K) return;
if(fill) best[wt] = min(best[wt], 1LL*d);
else ans = min(ans, best[K-wt] + 1LL*d);
for(auto &[u, t]: adj2[s]){
if(u == p or done[u]) continue;
calc(u, s, fill, d+1, wt+t);
}
}
void del(int s, int p, int d, int wt){
if(wt > K) return;
best[wt] = 1e18;
for(auto &[u, t]: adj2[s]){
if(u == p or done[u]) continue;
del(u, s, d+1, wt+t);
}
}
void centroid_decomp(int s){
int num = subtree_size(s, 0);
int cent = get_centroid(s, 0, num);
best[0] = 0;
for(auto &[u, w]: adj2[cent]){
if(done[u]) continue;
calc(u, cent, false, 1, w);
calc(u, cent, true, 1, w);
}
for(auto &[u, w]: adj2[cent]){
if(done[u]) continue;
del(u, cent, 1, w);
}
done[cent] = true;
for(auto u: adj[cent]){
if(!done[u]) centroid_decomp(u);
}
}
int best_path(int _N, int _K, int H[][2], int L[]){
N = _N, K = _K;
for(int i=0; i<N-1; i++){
int a = H[i][0], b = H[i][1], w = L[i];
a++; b++;
adj[a].pb(b); adj[b].pb(a);
adj2[a].pb({b, w}); adj2[b].pb({a, w});
}
fill(best, best+K+1, 1e18);
centroid_decomp(1);
if(ans == 1e18) ans = -1;
return ans;
}
