#include <bits/stdc++.h>
#include <race.h>
using namespace std;
using ll = long long;
#define fi first
#define se second
#define mp make_pair
#define eb emplace_back
#define ALL(x) (x).begin(), (x).end()
#define FOR(i, a, b) for(int i = (a); i < (b); ++i)
#define FORU(i, a, b) for(int i = (a); i <= (b); ++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
const int INF = 1e9;
const int N = 2e5 + 1;
const int K = 1e6;
int n, k;
using pi = pair<int, int>;
vector<pi> adj[N];
multiset<pi> s[N];
int ans = INF;
void dfs(int u, int p = -1){
s[u].insert({0, 0});
for(auto [w, v]: adj[u]) if(v != p){
dfs(v, u);
for(auto p: s[v]) if(p.fi + w <= k){
s[u].insert({p.fi + w, p.se + 1});
} else break;
}
for(auto [w, v]: adj[u]) if(v != p){
for(auto p: s[v]) if(p.fi + w <= k){
s[u].erase(s[u].find({p.fi + w, p.se + 1}));
} else break;
for(auto p: s[v]) if(p.fi + w <= k){
auto it = s[u].lower_bound({k - (p.fi + w), -1});
if(it == s[u].end()) continue;
if((*it).fi == k - (p.fi + w)){
ans = min(ans, p.se + 1 + (*it).se);
}
} else break;
for(auto p: s[v]) if(p.fi + w <= k){
s[u].insert({p.fi + w, p.se + 1});
} else break;
}
}
int best_path(int N, int K, int H[][2], int L[]){
n = N, k = K;
FOR(i, 0, N - 1){
adj[H[i][0]].eb(L[i], H[i][1]);
adj[H[i][1]].eb(L[i], H[i][0]);
}
dfs(0);
if(ans != INF) return ans;
return -1;
}
