#include <bits/stdc++.h>
#include "race.h"
#define ll long long
#define ld long double
#define sp ' '
#define en '\n'
#define smin(a, b) a = min(a, b)
#define smax(a, b) a = max(a, b)
using namespace std;
const int N = 5e5 + 2;
const int M = 1e9;
int mod = 1000000007;
vector<array<int, 2>> g[N];
bool was[N];
int sz[N], k;
void Dfs(int s, int e) {
sz[s] = 1;
for (auto u : g[s]) {
if (u[0] == e || was[u[0]]) continue;
Dfs(u[0], s);
sz[s] += sz[u[0]];
}
}
int Find(int s, int e, int n) {
for (auto u : g[s]) {
if (u[0] == e || was[u[0]]) continue;
if (2 * sz[u[0]] > n) return Find(u[0], s, n);
}
return s;
}
int FindCentroid(int s) {
Dfs(s, -1);
return Find(s, -1, sz[s]);
}
map<ll, int> m;
int ans;
vector<pair<ll, int>> tmp;
void Solve(int s, int e, int d, ll o) {
if (o > k || d > ans) return;
tmp.push_back({o, d});
if (m.find(k - o) != m.end()) smin(ans, d + m[k - o]);
for (auto u : g[s]) {
if (u[0] == e || was[u[0]]) continue;
Solve(u[0], s, d + 1, o + u[1]);
}
}
void Decompose(int s) {
s = FindCentroid(s);
was[s] = 1;
m.clear();
m[0] = 0;
for (auto u : g[s]) {
if (was[u[0]]) continue;
tmp.clear();
Solve(u[0], s, 1, u[1]);
for (auto v : tmp) {
if (m.find(v.first) == m.end()) m[v.first] = v.second;
else smin(m[v.first], v.second);
}
}
for (auto u : g[s]) {
if (was[u[0]] == 0) Decompose(u[0]);
}
}
int best_path(int n, int K, int h[][2], int l[]) {
k = K;
for (int i = 0; i < n - 1; i++) {
g[h[i][0]].push_back({h[i][1], l[i]});
g[h[i][1]].push_back({h[i][0], l[i]});
}
ans = n;
Decompose(0);
if (ans == n) ans = -1;
return ans;
}
