#include <bits/stdc++.h>
#define ve vector
#define ar array
#define pb push_back
#define ins insert
#define endl '\n'
#define ll long long
using namespace std;
const int MXN = 2e5+5;
ve<pair<int, ll>> adj[MXN];
ve<bool> proc(MXN, false);
ve<int> sz(MXN, 0);
int K;
int szdfs(int x, int p){
sz[x] = 1;
for(auto [i, _] : adj[x]){
if(i != p && !proc[i]){
szdfs(i, x);
sz[x] += sz[i];
}
}
return sz[x];
}
int find_centroid(int x, int n, int p){
for(auto [i, _] : adj[x]){
if(!proc[i] && i != p && sz[i] > n/2){
return find_centroid(i, n, x);
}
}
return x;
}
int ans = 1e9;
void upddfs(int x, int p, int cur, int down, map<int,int> &bk){
if(bk.count(cur)){
bk[cur] = min(bk[cur], down);
}
else{
bk[cur] = down;
}
for(auto [i, c] : adj[x]){
if(i != p && !proc[i] && cur + c <= K){
upddfs(i, x, cur + c, down+1, bk);
}
}
}
void chkdfs(int x, int p, int cur, int down, map<int, int> &bk){
if(bk.count(K-cur)){
ans = min(ans, down + bk[K-cur]);
}
for(auto [i, c] : adj[x]){
if(i != p && !proc[i] && cur + c <= K){
chkdfs(i, x, cur + c, down+1, bk);
}
}
}
void decompo(int x){
map<int, int> bk;
bk[0] = 0;
int cent = find_centroid(x, szdfs(x, -1), -1);
for(auto [i, c] : adj[cent]){
if(!proc[i]){
chkdfs(i, cent, c, 1, bk);
upddfs(i, cent, c, 1, bk);
}
}
proc[cent] = 1;
for(auto [i, _] : adj[cent]){
if(!proc[i]){
decompo(i);
}
}
}
int best_path(int N, int k, int H[][2], int L[]){
K = k;
for(int i = 0; i < N-1; i++){
adj[H[i][0]].pb({H[i][1], L[i]});
adj[H[i][1]].pb({H[i][0], L[i]});
}
szdfs(0, -1);
decompo(0);
if(ans == 1e9){
ans = -1;
}
return ans;
}
// int main(){
// int N, k;
// cin >> N >> k;
// int H[N-1][2];
// int L[N-1];
// for(int i = 0; i < N-1; i++){
// cin >> H[i][0] >> H[i][1] >> L[i];
// }
// cout << best_path(N, k, H, L)<<endl;
// }
