#include "race.h"
#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define ll long long
const int mxN = 2e5 + 5;
ll n,k,anss = 1e9,dis[mxN],d[mxN];
vector<pair<ll,ll>> v[mxN];
set<pair<ll,ll>> s[mxN];
void dfs(ll at, ll par){
s[at].insert({dis[at], d[at]});
for(auto it : v[at]){
if(it.first == par) continue;
d[it.first] = d[at] + 1;
dis[it.first] = dis[at] + it.second;
dfs(it.first, at);
}
for(auto it1 : v[at]){
ll it = it1.first;
if(it == par) continue;
if(s[at].size() < s[it].size()) swap(s[at], s[it]);
for(auto x : s[it]){
auto mn = s[at].lower_bound({dis[at] * 2 + k - x.first, 0LL});
if(mn == s[at].end()) continue;
pair<ll,ll> num = *mn;
if(num.first != dis[at] * 2 + k - x.first) continue;
anss = min(anss, x.second - 2 * d[at] + num.second);
}
for(auto x : s[it]) s[at].insert(x);
s[it].clear();
}
}
int best_path(int N, int K, int H[][2], int L[]){
n = N; k = K;
for(int i = 0; i < n - 1; i++){
v[H[i][0]].pb({H[i][1], L[i]});
v[H[i][1]].pb({H[i][0], L[i]});
}
dfs(1, 1);
if(anss == 1e9) return -1;
return anss;
}
