#include "bits/stdc++.h"
using namespace std;
#define pb push_back
#define pii pair<int, int>
#define fr first
#define sc second
const int inf = 1e9 + 7;
int best_path(int n, int k, int H[][2], int L[]){
vector <vector<pii>> pon(n);
for (int i = 0; i < n - 1; i++) {
pon[H[i][0]].pb({H[i][1], L[i]});
pon[H[i][1]].pb({H[i][0], L[i]});
}
vector <int> sz(n), ded(n);
function<void(int, int)> szdfs = [&](int u, int p) {
sz[u] = 1;
for (auto [v, w]: pon[u]) {
if (v == p || ded[v]) continue;
szdfs(v, u);
sz[u] += sz[v];
}
};
function<int(int, int, int)> findcentr = [&](int u, int p, int m) {
for (auto [v, w]: pon[u]) {
if (v == p || ded[v]) continue;
if (sz[v] > m / 2) return findcentr(v, u, m);
}
return u;
};
map <int, int> d;
function<void(int, int, int, int)> soldfs = [&](int u, int p, int c, int dep) {
if (d[k - c]) d[k] = (d[k] ? min(d[k], max(0, d[k - c]) + dep) : max(0, d[k - c]) + dep);
for (auto [v, w]: pon[u]) if (v != p && !ded[v]) soldfs(v, u, c + w, dep + 1);
};
function<void(int, int, int, int)> updatedfs = [&](int u, int p, int c, int dep) {
d[c] = (d[c] ? min(d[c], dep) : dep);
for (auto [v, w]: pon[u]) if (v != p && !ded[v]) updatedfs(v, u, c + w, dep + 1);
};
int ans = inf;
function<void(int)> sol = [&](int u) {
szdfs(u, u);
d.clear();
d[0] = -1;
for (auto [v, w]: pon[u]) {
if (ded[v]) continue;
soldfs(v, u, w, 1);
updatedfs(v, u, w, 1);
}
if (d[k]) ans = min(ans, d[k]);
ded[u] = 1;
for (auto [v, w]: pon[u]) if (!ded[v]) sol(findcentr(v, v, sz[v]));
};
sol(findcentr(0, 0, n));
return (ans == inf ? -1 : ans);
}
