#include <bits/stdc++.h>
#include "race.h"
using namespace std;
#define endl '\n'
#define ll long long
#define all(x) x.begin(), x.end()
vector<pair<int, int>> g[200005];
bool processed[200005];
int sz[200005];
int getSize(int cur, int par = -1) {
sz[cur] = 1;
for (auto next : g[cur]) {
if (next.first != par && !processed[next.first]) sz[cur] += getSize(next.first, cur);
}
return sz[cur];
}
int getCentroid(int cur, int des, int par = -1) {
for (auto next : g[cur]) {
if (next.first != par && !processed[cur] && sz[cur] > des / 2) return getCentroid(next.first, des, cur);
}
return cur;
}
int ans = 10e7, k;
unordered_map<int, int> cnt;
void solve(int cur, int par, int depth, int sum, bool t) {
if (sum > k || depth >= ans) return;
if (sum == k) {
ans = depth;
return;
}
if (!t) {
if (cnt.count(k - sum)) ans = min(ans, depth + cnt[k - sum]);
}
else {
if (!cnt.count(sum)) cnt[sum] = depth;
else cnt[sum] = min(cnt[sum], depth);
}
for (auto next : g[cur]) {
if (next.first != par && !processed[next.first] && sum + next.second <= k) {
solve(next.first, cur, depth + 1, sum + next.second, t);
}
}
}
void decompose(int cur = 0) {
getSize(cur);
cur = getCentroid(cur, getSize(cur));
processed[cur] = 1;
for (auto next : g[cur]) {
if (!processed[next.first] && next.second <= k) {
solve(cur, -1, 1, next.second, 0);
solve(cur, -1, 1, next.second, 1);
}
}
cnt.clear();
for (auto next : g[cur]) {
if (!processed[next.first]) decompose(next.first);
}
}
int best_path(int N, int K, int H[][2], int L[]) {
k = K;
ans = N;
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]});
}
decompose();
if (ans == N) return -1;
else return ans;
}
