#include <bits/stdc++.h>
using namespace std;
const int MAX = 2e5 + 5;
vector<pair<int, int>> g[MAX];
int k, ans = 1e9;
bitset<MAX> deleted;
struct cal {
unordered_map<int, int> mp;
void update(int u, int p, int sum, int depth) {
if (sum > k) return;
auto &cur = mp[sum];
if (cur == 0) cur = depth;
else cur = min(cur, depth);
for (auto &[v, w] : g[u]) {
if (v != p && !deleted[v]) {
update(v, u, sum + w, depth + 1);
}
}
}
void add(int u, int p, int sum, int depth) {
if (sum > k) return;
auto it = mp.find(k - sum);
if (it != mp.end()) ans = min(ans, it->second + depth);
for (auto &[v, w] : g[u]) {
if (v != p && !deleted[v]) {
add(v, u, sum + w, depth + 1);
}
}
}
void lamviec(int u) {
mp[0] = 0;
for (auto &[v, w] : g[u]) {
if (!deleted[v]) {
add(v, u, w, 1);
update(v, u, w, 1);
}
}
}
};
int sz[MAX];
void dfs(int u, int p) {
sz[u] = 1;
for (auto &[v, w] : g[u]) {
if (v != p && !deleted[v]) {
dfs(v, u);
sz[u] += sz[v];
}
}
}
int findcentroid(int u, int p, const int &n) {
for (auto &[v, w] : g[u]) {
if (v != p && !deleted[v] && sz[v] * 2 > n) return findcentroid(v, u, n);
}
return u;
}
void decompose(int u) {
dfs(u, 0);
u = findcentroid(u, 0, sz[u]);
deleted[u] = true;
cal tmp; tmp.lamviec(u);
for (auto &[v, w] : g[u]) {
if (!deleted[v]) {
decompose(v);
}
}
}
int best_path(int N, int K, int H[][2], int L[]) {
int n = N;
k = K;
for (int u, v, w, i = 0; i < n - 1; i++) {
u = H[i][0], v = H[i][1], w = L[i];
++u, ++v;
g[u].emplace_back(v, w);
g[v].emplace_back(u, w);
}
decompose(1);
if (ans == (int)1e9) ans = -1;
return ans;
}
