#include "race.h"
#include <bits/stdc++.h>
using namespace std;
using pii = pair<int, int>;
const int inf = 1e9;
const int MxN = 2e5 + 10;
const int MxL = 1e6 + 10;
int n, k, ans, sz[MxN], cnt[MxL];
bool used[MxN];
vector<int> res2;
vector<pii> res, adj[MxN];
int dfssz(int u, int p) {
sz[u] = 1;
for (auto [v, w] : adj[u]) if (v != p && !used[v]) sz[u] += dfssz(v, u);
return sz[u];
}
int centroid(int u, int p, int n) {
for (auto [v, w] : adj[u]) if (v != p && !used[v] && sz[v] > n / 2) return centroid(v, u, n);
return u;
}
void dfs(int u, int p, int d, int l) {
if (l > k) return;
ans = min(ans, d + cnt[k - l]);
res.push_back({l, d});
res2.push_back(l);
for (auto [v, w] : adj[u]) if (v != p && !used[v]) dfs(v, u, d + 1, l + w);
}
void decom(int u) {
u = centroid(u, -1, dfssz(u, -1));
used[u] = true;
for (auto [v, w] : adj[u]) {
if (used[v]) continue;
dfs(v, u, 1, w);
for (auto [l, d] : res) cnt[l] = min(cnt[l], d);
res.clear();
}
for (auto l : res2) cnt[l] = n;
res2.clear();
for (auto [v, w] : adj[u]) if (!used[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++) {
int u = H[i][0];
int v = H[i][1];
int w = L[i];
adj[u].push_back({v, w});
adj[v].push_back({u, w});
}
for (int i = 1; i <= k; i++) cnt[i] = n;
ans = n;
decom(0);
return ans != n ? ans : -1;
}
