//#include "race.h"
#include <bits/stdc++.h>
using namespace std;
const int mxN=2e5+1, INF=1e9;
int k, ans=INF, sz[mxN];
vector<pair<int, int>> adj[mxN], vals;
map<int, int> mn;
bool vis[mxN];
int dfs_sz(int v, int p=-1) {
sz[v]=1;
for (auto [u, d]:adj[v])
if (!vis[u] && u^p)
sz[v]+=dfs_sz(u, v);
return sz[v];
}
int dfs_centroid(int tot, int v, int p=-1) {
for (auto [u, d]:adj[v])
if (!vis[u] && u^p && sz[u]*2>tot)
return dfs_centroid(tot, u, v);
return v;
}
void dfs(int v, int len, int p=-1, int dep=1) {
vals.emplace_back(dep, len);
for (auto [u, d]:adj[v])
if (!vis[u] && u^p && len+d<=k)
dfs(u, len+d, v, dep+1);
}
void decomp(int x=0) {
int v=dfs_centroid(dfs_sz(x), x);
vis[v]=1;
mn.clear();
mn[0]=0;
for (auto [u, d]:adj[v]) {
if (vis[u])
continue;
vals.clear();
dfs(u, d);
for (auto [dep, len]:vals)
if (mn.count(k-len))
ans=min(ans, dep+mn[k-len]);
for (auto [dep, len]:vals) {
if (mn.count(len))
mn[len]=min(mn[len], dep);
else
mn[len]=dep;
}
}
for (auto [u, d]:adj[v])
if (!vis[u])
decomp(u);
}
int best_path(int N, int K, int H[][2], int L[]) {
k=K;
for (int i=0; i<N; ++i)
adj[i].clear();
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]);
}
decomp();
return (ans==INF?-1:ans);
}
