#include<bits/stdc++.h>
using namespace std;
const int lim = 200000;
vector<pair<int, int>> adj[lim + 5];
map<int, int> paths[lim + 5];
int n, k, answer = 1e9;
void dfs(int cur = 1, int par = -1){
for(pair<int, int> ch : adj[cur]){
if(ch.first == par)continue;
dfs(ch.first, cur);
if((int)paths[ch.first].size() > (int)paths[cur].size()){
paths[cur].swap(paths[ch.first]);
}
for(pair<int, int> elem : paths[ch.first]){
if(paths[cur].count(k - elem.first - ch.second)){
answer = min(answer, elem.second + 1 + paths[cur][k - elem.first - ch.second]);
}
}
for(pair<int, int> elem : paths[ch.first]){
if(elem.first + ch.second > k)continue;
if(!paths[cur].count(elem.first + ch.second)){
paths[cur][elem.first + ch.second] = elem.second + 1;
}
else paths[cur][elem.first + ch.second] = min(paths[cur][elem.first + ch.second], elem.second + 1);
}
paths[ch.first].clear();
}
}
int best_path(int N, int K, int H[][2], int L[]){
n = N; k = K;
for(int i = 0; i < N-1; ++i){
int u = H[i][0] + 1, v = H[i][1] + 1;
adj[u].push_back(make_pair(v, L[i]));
adj[v].push_back(make_pair(u, L[i]));
}
for(int i = 1; i <= N; ++i){
paths[i][0] = 0;
}
dfs();
return (answer == 1e9 ? -1 : answer);
}
