#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int MAXN = 2e5+5;
vector<pair<ll,ll>> adj[MAXN]; //first second node, then weight of the edge
map<ll,ll> mindist[MAXN];
ll dep[MAXN],weight[MAXN];
int K; ll ans = 1e18;
void dfs(int u, int p){
for(auto x : adj[u]){
if(p != x.first){
dep[x.first] = dep[u]+1;
weight[x.first] = weight[u]+x.second;
mindist[x.first][weight[x.first]] = dep[x.first];
//cout << x.first << " " << dep[x.first] << " " << weight[x.first] << " " << "\n";
dfs(x.first,u);
}
}
}
void smalltolarge(int u, int p){
ll F = K+2*weight[u];
for(auto x : adj[u]){
if(x.first != p){
int v = x.first;
smalltolarge(v,u);
if(mindist[v].size() > mindist[u].size()){
swap(mindist[v],mindist[u]);
}
//cout << u << " " << v << "\n";
for(auto m : mindist[v]){
if(mindist[u].find(F-m.first) != mindist[u].end()){
ans = min(ans,mindist[u][F-m.first]+m.second-2*dep[u]);
}
}
for(auto m : mindist[v]){
if(mindist[u].find(m.first) == mindist[u].end()){
mindist[u][m.first] = m.second;
}
else{
mindist[u][m.first] = min(mindist[u][m.first],m.second);
}
//cout << m.first << " " << mindist[u][m.first] << " ";
}
}
}
}
int best_path(int n, int k, int h[][2], int length[]){
K = k;
for(int i = 0;i<n-1;++i){
int u = h[i][0], v = h[i][1];
adj[u].push_back({v,length[i]});
adj[v].push_back({u,length[i]});
}
mindist[0][0] = 0;
dfs(0,-1);
smalltolarge(0,-1);
if(ans != 1e18) return ans;
else return -1;
}
