/*Author: KawakiMeido*/
#include <bits/stdc++.h>
#include "race.h"
#define pb push_back
#define endl "\n"
#define ll long long
#define all(x) (x).begin(),(x).end()
#define pii pair<int,int>
#define fi first
#define se second
#define TEXT ""
using namespace std;
/*Constants*/
const int N = 2e5+10;
const int INF = 1e9+7;
const long long LLINF = 1e18+3;
/*Global Variables*/
int n,k;
vector<pii> adj[N];
int sz[N];
bool vis[N];
int ans;
map<int,int> mp;
int findSize(int u, int p=0){
sz[u] = 1;
for (auto [v,w]:adj[u]){
if (vis[v] || v==p) continue;
sz[u]+=findSize(v,u);
}
return sz[u];
}
int findCentroid(int u, int n, int p=0){
for (auto [v,w]:adj[u]){
if (vis[v] || v==p) continue;
if (sz[v] > n/2) return findCentroid(v,n,u);
}
return u;
}
void dfsCalc(int u, int dist, int p=0, int depth = 1){
if (k-dist>=0 && mp.count(k-dist)){
ans = min(ans,depth + mp[k-dist]);
}
// cout << u << " " << ans << endl;
for (auto [v,w]:adj[u]){
if (vis[v] || v==p) continue;
dfsCalc(v,dist+w,u,depth+1);
}
}
void dfsIns(int u, int dist, int p=0, int depth = 1){
if (!mp.count(dist)) mp[dist] = depth;
else mp[dist] = min(mp[dist],depth);
for (auto [v,w]:adj[u]){
if (vis[v] || v==p) continue;
dfsIns(v,dist+w,u,depth+1);
}
}
void buildCentroid(int u, int p=0){
findSize(u);
int c = findCentroid(u,sz[u]);
// cout << "centroid: " << c << endl;
vis[c] = true;
mp[0] = 0;
for (auto [v,w]:adj[c]){
if (vis[v]) continue;
dfsCalc(v,w);
dfsIns(v,w);
}
// cout << ans << endl;
mp.clear();
for (auto [v,w]:adj[c]){
if (vis[v]) continue;
buildCentroid(v,c);
}
}
signed 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,v;
u = h[i][0];
v = h[i][1];
++u;
++v;
// tie(u,v) = h[i];
adj[u].push_back({v,l[i]});
adj[v].push_back({u,l[i]});
}
ans = n+1;
buildCentroid(1);
if (ans == n+1) return -1;
return ans;
}
//int _n, _k;
//int _h[N][2];
//int _l[N];
//void solve(){
// cin >> _n >> _k;
// for (int i=0; i<_n-1; i++){
// int u,v,w;
// cin >> u >> v >> w;
// _h[i][0] = u;
// _h[i][1] = v;
// _l[i] = w;
// }
// cout << best_path(_n,_k,_h, _l);
//}
//
//signed main(){
// cin.tie(0) -> sync_with_stdio(0);
// if (fopen(TEXT".inp","r")){
// freopen(TEXT".inp","r",stdin);
// freopen(TEXT".out","w",stdout);
// }
//
// int testCount = 1;
//// cin >> testCount;
// while (testCount--){
// solve();
// }
//
// return 0;
//}
