#include <iostream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <numeric>
#include <cstring>
#include <string>
#include <cmath>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
using namespace std;
#define ll long long
#define ull unsigned long long
#define f first
#define s second
#define PF push_front
#define PB push_back
#define MP make_pair
#define pi pair<int, int>
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define max(a, b) ((a > b)? a : b)
#define min(a, b) ((a < b)? a : b)
#define max3(a, b, c) max(max(a, b), c)
#define min3(a, b, c) min(min(a, b), c)
const int N = 2e5 + 5;
const int M = 1e9 + 7;
const int inf = 0x3f3f3f3f;
const ll int INF = 1e18;
int _n, _k;
map<int, int> mp;
vector<pi> adj[N];
vector<int> sz(N), val(N);
vector<bool> processed(N, false);
int get_subtree_size(int cur, int prev = -1){
sz[cur] = 1;
for(auto [child, _] : adj[cur]){
if(processed[child] || child == prev) continue;
sz[cur] += get_subtree_size(child, cur);
}
return sz[cur];
}
int get_centroid(int thres, int cur, int prev = -1){
for(auto [child, _] : adj[cur]){
if(processed[child] || child == prev) continue;
if(sz[child] >= thres) return get_centroid(thres, child, cur);
}
return cur;
}
int ans = N;
void get_cnt(int cur, int prev, bool filling, int depth, int cnt = 1){
if(depth > _k) return;
if(filling){
if(mp[depth] == 0) mp[depth] = cnt;
else mp[depth] = min(mp[depth], cnt);
}else {
int tmp = mp[_k - depth];
if(mp[tmp]) ans = min(ans, cnt + mp[tmp]);
}
for(auto [child, w] : adj[cur]){
if(processed[child] || child == prev) continue;
get_cnt(child, cur, filling, depth+w, cnt+1);
}
}
void centroid_decomp(int node = 1){
int centroid = get_centroid(get_subtree_size(node) >> 1, node);
processed[centroid] = true;
mp.clear();
for(auto [child, w] : adj[centroid]){
if(processed[child]) continue;
get_cnt(child, centroid, false, w);
get_cnt(child, centroid, true, w);
}
for(auto [child, _] : adj[centroid]){
if(!processed[child]) centroid_decomp(child);
}
}
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 a = H[i][0], b = H[i][1];
adj[a].PB({b, L[i]});
adj[b].PB({a, L[i]});
}
centroid_decomp();
if(ans == N) ans = -1;
return ans;
}
