#include <bits/stdc++.h>
// mrrrow meeow :3
// go play vivid/stasis now! it's free on steam
#define fo(i, a, b) for (auto i = (a); i < (b); i++)
#define of(i, a, b) for (auto i = (b); i-- > (a);)
#define f first
#define s second
#define pb push_back
#define pob pop_back
#define lb lower_bound
#define ub upper_bound
#define be(a) a.begin(), a.end()
using namespace std;
int ____init = [] {
ios::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
return 0;
}();
vector<pair<int, int>> adj[200000];
int dfs(int i, int d, int p = -1) {
if (d == 0) return 0;
if (d < 0) return 1000000;
int md = 1000000;
for (auto [j, l] : adj[i]) {
if (j == p) continue;
md = min(md, dfs(j, d - l, i));
}
return md + 1;
}
int best_path(int n, int k, int h[][2], int l[]) {
fo(i, 0, n - 1) {
adj[h[i][0]].pb({h[i][1], l[i]});
adj[h[i][1]].pb({h[i][0], l[i]});
}
int res = 1000000;
fo(i, 0, n) {
res = min(res, dfs(i, k));
}
return res == 1000000 ? -1 : res;
}
