#include <iostream>
#include <vector>
#include <algorithm>
#include <cstring>
#include <queue>
#include <set>
#include <map>
#define INF 1e9
using namespace std;
typedef long long ll;
int n, k;
int ans = INF;
vector<pair<int, int>>adj[200005];
bool visited[200005];
ll dp[200005];
vector<int>v;
vector<int>cnt(1e6 + 5, 1e9);
int get_size(int s, int e) {
dp[s] = 1;
for (auto u : adj[s]) {
if (u.first == e || visited[u.first]) continue;
get_size(u.first, s);
dp[s] += dp[u.first];
}
return dp[s];
}
int get_centroid(int s, int e, int n) {
for (auto u : adj[s]) {
if (u.first == e || visited[u.first]) continue;
if (dp[u.first] * 2 > n)return get_centroid(u.first, s, n);
}
return s;
}
void dfs(int s, int e, ll l, int d, bool mode) {
if (l > k)return;
for (pair<int,int> x : adj[s]) {
if (!visited[x.first] && x.first != e) {
dfs(x.first, s, l + x.second, d + 1, mode);
}
}
if (!mode) {
ll need = k - l;
if (cnt[need] != 1e9) {
ans = min(ans, d + cnt[need]);
}
}
else {
cnt[l] = min(cnt[l], d);
v.push_back(l);
}
}
void centroid_decomposition(int node) {
int centroid = get_centroid(node, 0, get_size(node, 0));
visited[centroid] = true;
cnt[0] = 0;
for (pair<int,int> u : adj[centroid]) {
if (!visited[u.first]) {
dfs(u.first, centroid, u.second, 1, false);
dfs(u.first, centroid, u.second, 1, true);
}
}
for (auto u : v) cnt[u] = INF;
v.clear();
for (auto u : adj[centroid]) {
if (!visited[u.first])centroid_decomposition(u.first);
}
}
int best_path(int N, int K, int h[][2], int l[]) {
n = N; k = K;
for (int i = 1; i <= n - 1; i++) {
int u = h[i][0], v = h[i][1], w = l[i];
adj[u].push_back({ v, w });
adj[v].push_back({ u, w });
}
centroid_decomposition(1);
if (ans == 1e9) return -1;
else return ans;
}
