#include <bits/stdc++.h>
using namespace std;
#define dbg(x) cerr << #x << ": " << x << endl;
const int MAX_N = 200'000;
const int INF = 1e9;
vector<pair<int, int>> g[MAX_N];
unordered_map<long long, int> s[MAX_N];
int depth[MAX_N];
long long len[MAX_N];
int ans = INF;
int k;
template<typename T>
void merge(T& lhs, T& rhs, int v) {
if (lhs.size() > rhs.size()) {
swap(lhs, rhs);
}
for (const auto& [curr_len, curr_depth] : lhs) {
long long need_find = k + 2 * len[v] - curr_len;
if (rhs.find(need_find) != rhs.end()) {
ans = min(ans, curr_depth + rhs.at(need_find) - 2 * depth[v]);
}
}
for (const auto& [key, value] : lhs) {
if (rhs.find(key) == rhs.end()) {
rhs[key] = value;
} else {
rhs[key] = min(rhs[key], value);
}
}
}
void dfs(int v = 0, int p = -1) {
s[v][len[v]] = depth[v];
for (const auto& [u, weight] : g[v]) {
if (u != p) {
depth[u] = depth[v] + 1;
len[u] = len[v] + weight;
dfs(u, v);
merge(s[u], s[v], v);
}
}
}
int best_path(int n, int curr_k, int highways[][2], int length[]) {
for (int i = 0; i < n - 1; ++i) {
auto [u, v] = highways[i];
g[u].emplace_back(v, length[i]);
g[v].emplace_back(u, length[i]);
}
k = curr_k;
dfs();
if (ans == INF) ans = -1;
return ans;
}
// int main() {
// int n;
// cin >> n;
// cin >> k;
// for (int i = 0; i < n - 1; ++i) {
// int u, v, w;
// cin >> u >> v >> w;
// g[u].emplace_back(v, w);
// g[v].emplace_back(u, w);
// }
// dfs();
// cout << ans << '\n';
// }
/*
4 3
0 1 1
1 2 2
1 3 4
2
*/
