#include <bits/stdc++.h>
#define name ""
//#define int long long
#define ll long long
using namespace std;
const int maxn = 2e5 + 10;
int n , k , h[maxn] , cost[maxn] , res = -1;
vector<vector<pair<int , int>>> g(maxn);
vector<map<ll , ll>> mp;
void pre(int u , int p , int sum , int dep){
mp[u][sum] = dep;
cost[u] = sum;
h[u] = dep;
for(auto e : g[u]){
int v = e.first;
if(v == p) continue;
pre(v , u , sum + e.second , dep + 1);
}
}
void dfs(int u , int p){
for(auto e : g[u]){
int v = e.first;
if(v == p) continue;
dfs(v , u);
if(mp[u].size() < mp[v].size()) swap(mp[u] , mp[v]);
for(auto x : mp[v]){
auto it = mp[u].find(k + 2 * cost[u] - x.first);
if(it != mp[u].end()){
int c = it->second + x.second - 2 * h[u];
res = (res == -1 ? c : min(res , c));
}
}
for(auto x : mp[v]){
auto it = mp[u].find(x.first);
if(it == mp[u].end()) mp[u].insert(x);
else mp[u][x.first] = min(mp[u][x.first] , x.second); // uu tien h cao nhat
}
}
}
int best_path(int nn , int kk , int h[][2] , int l[]){
n = nn , k = kk;
// cout << n <
mp.resize(n + 10);
for(int i = 0 ; i < n - 1 ; i ++){
int u = h[i][0] , v = h[i][1];
++u , ++v;
g[u].push_back({v , l[i]});
g[v].push_back({u , l[i]});
}
pre(1 , 0 , 0 , 0);
dfs(1 , 0);
return res;
}
