#include "race.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
#define X first
#define Y second
#define sep ' '
#define debug(x) cerr << #x << ": " << x << endl;
const ll INF = 1e9;
const ll MAXN = 1e6 + 10;
int n, k, ans, sz[MAXN];
vector<pll> adj[MAXN];
bool B[MAXN];
map<ll, int> mp;
vector<pll> vec;
int sub_sz(int v, int p) {
sz[v] = 1;
for (auto [u, w] : adj[v])
if (!B[u] && u != p)
sz[v] += sub_sz(u, v);
return sz[v];
}
int centroid(int v, int p, int n) {
for (auto [u, w] : adj[v])
if (!B[u] && u != p && sz[u] * 2 > n)
return centroid(u, v, n);
return v;
}
void dfs(int v, int p, ll w, int l) {
vec.push_back({w, l});
auto it = mp.find(k - w);
if (it != mp.end()) ans = min(ans, l + it -> Y);
for (auto [u, e_w] : adj[v])
if (u != p && !B[u])
dfs(u, v, w + e_w, l + 1);
}
void solve(int v) {
B[v = centroid(v, 0, sub_sz(v, 0))] = true;
mp.clear();
mp[0] = 0;
for (auto [u, w] : adj[v]) {
if (!B[u]) {
dfs(u, v, w, 1);
for (pll e : vec) {
auto it = mp.find(e.X);
if (it == mp.end() || it -> Y > e.Y)
mp[e.X] = e.Y;
}
vec.clear();
}
}
for (auto [u, w] : adj[v])
if (!B[u])
solve(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 u = H[i][0], v = H[i][1], l = L[i];
u++, v++;
adj[u].push_back({v, l});
adj[v].push_back({u, l});
}
ans = INF;
solve(1);
return (ans == INF ? -1 : ans);
}
