#include <bits/stdc++.h>
using namespace std;
const int MAXN = 2e5;
vector<pair<int, int>> adj[MAXN];
unordered_map<long long, int> dists[MAXN];
int solve(int u, int p, int currDepth, long long currDist, int K) {
int res = INT_MAX;
dists[u][currDist] = currDepth;
for (auto [v, w] : adj[u]) {
if (v != p) {
res = min(res, solve(v, u, currDepth + 1, currDist + w, K));
if (dists[u].size() < dists[v].size()) swap(dists[u], dists[v]);
for (auto [dist, depth] : dists[v])
if (auto it = dists[u].find(K + 2 * currDist - dist); it != dists[u].end())
res = min(res, depth + it->second - 2 * currDepth);
for (auto [dist, depth] : dists[v])
if (dists[u].count(dist))
dists[u][dist] = min(dists[u][dist], depth);
else
dists[u][dist] = depth;
}
}
return res;
}
int best_path(int N, int K, int H[][2], int L[]) {
for (int i = 0; i < N - 1; ++i)
for (int j = 0; j < 2; ++j)
adj[H[i][j]].push_back({H[i][j ^ 1], L[i]});
if (int res = solve(0, 0, 0, 0, K); res != INT_MAX) return res;
return -1;
}
