#include <bits/stdc++.h>
#include "race.h"
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define REP(i, n) FOR(i, 0, n)
#define ll long long
using namespace std;
const int MAXN = 200100;
vector <pair <int, int> > ve[MAXN];
int sub[MAXN];
int bio[MAXN], cnt;
int n, k;
int out_len = MAXN;
int len[5 * MAXN];
int date[5 * MAXN];
int num;
int tmp;
void rek1(int x, int l, int di) {
if (l > k) return;
if (k >= l && date[k - l] == num) {
out_len = min(out_len, di + len[k - l]);
}
bio[x] = cnt;
for (auto tr : ve[x]) {
int y = tr.first, d = tr.second;
if (bio[y] >= cnt) continue;
rek1(y, l + d, di + 1);
}
return;
}
void rek2(int x, int l, int di) {
if (l > k) return;
if (date[l] < num) {
date[l] = num;
len[l] = 1e9;
}
len[l] = min(len[l], di);
bio[x] = cnt;
for (auto tr : ve[x]) {
int y = tr.first, d = tr.second;
if (bio[y] >= cnt) continue;
rek2(y, l + d, di + 1);
}
return;
}
void solve(int x) {
bio[x] = 1e9;
num++;
cnt++;
date[0] = num, len[0] = 0;
for (auto tr : ve[x]) {
int y = tr.first, d = tr.second;
if (bio[y] >= cnt) continue;
rek1(y, d, 1);
cnt++;
rek2(y, d, 1);
cnt++;
}
return;
}
int si;
void dfs(int x) {
si++;
bio[x] = cnt;
sub[x] = 1;
for (auto tr : ve[x]) {
int y = tr.first;
if (bio[y] >= cnt) continue;
dfs(y);
sub[x] += sub[y];
}
return;
}
int find_centroid(int x) {
bio[x] = cnt;
for (auto tr : ve[x]) {
int y = tr.first;
if (bio[y] >= cnt) continue;
if (sub[y] > si / 2) return find_centroid(y);
}
return x;
}
void decompose(int x) {
cnt++, si = 0;
dfs(x);
cnt++;
int c = find_centroid(x);
solve(c);
for (auto tr : ve[c]) {
int y = tr.first;
if (bio[y] != 1e9) decompose(y);
}
return;
}
int best_path(int N, int K, int H[][2], int L[]) {
n = N, k = K;
REP(i, n) {
int a = H[i][0], b = H[i][1], c = L[i];
ve[a].push_back({b, c});
ve[b].push_back({a, c});
}
decompose(0);
if (out_len == MAXN) return -1;
return out_len;
}
