#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <iomanip>
#include <numeric>
#include <vector>
#include <queue>
#include <stack>
#include <string>
#include <set>
#include <unordered_map>
#include "race.h"
#define hyathu main
#define popcorn __builtin_popcount
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
constexpr int mmb = 1e5 + 69;
const ld pi = atan(1) * 4;
vector <pair <int, ll>> v[mmb];
int p[mmb];
unordered_map <ll, int> dist[mmb];
ll d[mmb], K;
int h[mmb];
int ans = 2e9;
void dfs(int i){
unordered_map <ll, int> &cur = dist[i];
cur.emplace(d[i], h[i]);
for(pair <int, ll> &adj : v[i]){
int nx = adj.first;
ll ad = adj.second;
if(nx == p[i]) continue;
p[nx] = i;
d[nx] = d[i] + ad;
h[nx] = h[i] + 1;
dfs(nx);
for(pair <const ll, int> &dst : dist[nx]){
ll ds = dst.first;
int hs = dst.second;
auto it = cur.find(K - ds + 2 * d[i]);
if(it != cur.end())
ans = min(ans, hs + it->second - 2 * h[i]);
}
for(pair <const ll, int> &dst : dist[nx]){
ll ds = dst.first;
int hs = dst.second;
auto res = cur.insert(dst);
if(!res.second) res.first->second = min(res.first->second, hs);
}
dist[nx].clear();
}
}
int best_path(int n, int k, int h[][2], int l[]){
fill(p, p + n, -1);
K = k;
for(int i = 0; i < n - 1; ++i){
v[h[i][0]].emplace_back(h[i][1], l[i]);
v[h[i][1]].emplace_back(h[i][0], l[i]);
}
dfs(0);
return (ans == 2e9 ? -1 : ans);
}
