#include <bits/stdc++.h>
using namespace std;
#define int long long
const int MAX = 2e5 + 24;
int sze[MAX];
bitset <MAX> vis;
int k;
vector <pair <int, int>> adj[MAX];
void calc (int pos, int par) {
sze[pos] = 1;
for (auto j : adj[pos]) {
if (j.first == par || vis[j.first]) continue;
calc(j.first, pos);
sze[pos] += sze[j.first];
}
}
int find (int pos, int par, int kk) {
for (auto j : adj[pos]) {
if (j.first == par) continue;
if (vis[j.first]) continue;
if (sze[j.first] > (kk >> 1)) return find(j.first, pos, kk);
}
return pos;
}
int mn = 1e10;
map <int, int> cnt;
void ll2 (int pos, int par, int dep, int dist) {
if (dist > k) return;
if (cnt.count(k - dist)) mn = min(cnt[k - dist] + dep, mn);
for (auto j : adj[pos]) {
if (j.first != par && !vis[j.first]) {
ll2(j.first, pos, dep + 1, dist + j.second);
}
}
}
void ll (int pos, int par, int dep, int dist) {
if (dist > k) return;
if (cnt.count(dist)) cnt[dist] = min(cnt[dist], dep);
else cnt[dist] = dep;
for (auto j : adj[pos]) {
if (j.first != par && !vis[j.first]) {
ll(j.first, pos, dep + 1, dist + j.second);
}
}
}
void decomp (int pos) {
calc(pos, -1);
int c = find(pos, -1, sze[pos]);
vis[c] = 1;
cnt[0] = 0;
for (auto j : adj[c]) {
if (vis[j.first]) continue;
ll2(j.first, c, 1, j.second);
ll(j.first, c, 1, j.second);
}
cnt.clear();
for (auto i : adj[c]) {
if (!vis[i.first]) {
decomp(i.first);
}
}
}
int32_t best_path (int32_t n, int32_t K, int32_t h[][2], int32_t l[]) {
k = K;
for (int i = 0; i + 1 < n; i++) {
adj[h[i][0] + 1].push_back({h[i][1] + 1, l[i]});
adj[h[i][1] + 1].push_back({h[i][0] + 1, l[i]});
}
for (int i = 1; i <= n; i++) {
vis[i] = 0;
}
decomp(1);
return (mn >= 1e10 ? -1 : mn);
}
