#include "race.h"
#include <bits/stdc++.h>
using namespace std;
const int mxN = 2e5;
int n, k, ans = INT_MAX, sz[mxN], vis[mxN], mn[5 * mxN + 1];
vector<pair<int, int>> g[mxN];
int dfssz(int u, int p){
sz[u] = 1;
for(auto [v, w] : g[u]) if(v != p && !vis[v]) sz[u] += dfssz(v, u);
return sz[u];
}
int findcentroid(int u, int p, int rtsz){
for(auto [v, w] : g[u]) if(v != p && !vis[v] && sz[v] * 2 > rtsz) return findcentroid(v, u, rtsz);
return u;
}
void dfsadd(int u, int p, int cur, int d){
if(cur > k) return;
mn[cur] = min(mn[cur], d);
for(auto [v, w] : g[u]) if(v != p && !vis[v]) dfsadd(v, u, cur + w, d + 1);
}
void dfsrem(int u, int p, int cur){
if(cur > k) return;
mn[cur] = INT_MAX;
for(auto [v, w] : g[u]) if(v != p && !vis[v]) dfsrem(v, u, cur + w);
}
void dfsqry(int u, int p, int cur, int d){
if(cur > k) return;
if(mn[k - cur] != INT_MAX){
ans = min(ans, d + mn[k - cur]);
}
for(auto [v, w] : g[u]) if(v != p && !vis[v]) dfsqry(v, u, cur + w, d + 1);
}
void decom(int u){
int rtsz = dfssz(u, -1);
u = findcentroid(u, -1, rtsz);
vis[u] = 1;
mn[0] = 0;
for(auto [v, w] : g[u]){
if(!vis[v]){
dfsqry(v, u, w, 1);
dfsadd(v, u, w, 1);
}
}
for(auto [v, w] : g[u]) if(!vis[v]) dfsrem(v, u, w);
mn[0] = INT_MAX;
for(auto [v, w] : g[u]) if(!vis[v]) decom(v);
}
int best_path(int N, int K, int H[][2], int L[]){
n = N, k = K;
for(int i = 0;i<N - 1;i++){
g[H[i][0]].push_back({H[i][1], L[i]});
g[H[i][1]].push_back({H[i][0], L[i]});
}
for(int i = 0;i<=5 * mxN;i++) mn[i] = INT_MAX;
decom(0);
return (ans == INT_MAX ? -1 : ans);
}
