#include <bits/stdc++.h>
using namespace std;
#ifndef wambule
#include "race.h"
#endif
const int N = 200005, K = 1000006;
int mn, globk, ak[K], fp = -1;
vector<pair<int, int>> v[N], ve;
bool bo[N];
inline void minn(int &a, int b) {
if(a == -1 || b < a) a = b;
}
int ctr(int dg, int op) {
int *dr = new int, *y = new int;
*dr = mn - 1;
bool *mo = new bool;
*mo = 1;
for(int i = 0; i < v[dg].size(); ++i) {
if(v[dg][i].first != op && !bo[v[dg][i].first]) {
*y = ctr(v[dg][i].first, dg);
if(*y < 0) return *y;
if(*y > mn / 2) *mo = 0;
*dr -= *y;
}
}
if(*dr > mn / 2) *mo = 0;
if(*mo) return (delete dr, delete y, delete mo, -dg);
mn -= *dr;
return (delete dr, delete y, delete mo, mn);
}
int sra(int dg, int op) {
int *dr = new int;
*dr = 1;
for(int i = 0; i < v[dg].size(); ++i) {
if(v[dg][i].first != op && !bo[v[dg][i].first]) {
*dr += sra(v[dg][i].first, dg);
}
}
dg = *dr;
delete dr;
return dg;
}
int cntr(int x = 0) {
mn = sra(x, -1);
return -ctr(x, -1);
}
void ovo(int dg, int op, int wr, int md) {
// cout << "[ovog] " << dg << "\n";
if(md > globk) return;
ve.push_back({wr, md});
for(int i = 0; i < v[dg].size(); ++i) {
if(v[dg][i].first != op && !bo[v[dg][i].first]) {
ovo(v[dg][i].first, dg, wr + 1, md + v[dg][i].second);
}
}
}
void ama(int dg) {
// cout << "[cntr] " << dg << "\n";
bo[dg] = 1;
stack<int> vey;
for(int i = 0; i < v[dg].size(); ++i) {
if(!bo[v[dg][i].first]) {
ve.clear();
ovo(v[dg][i].first, -1, 1, v[dg][i].second);
for(int j = 0; j < ve.size(); ++j) {
// cout << "[vepm] " << ve[i].first << " " << ve[i].second << "\n";
if(ve[j].second == globk) minn(fp, ve[j].first);
else {
vey.push(ve[j].second);
if(ak[globk - ve[j].second]) {
minn(fp, ak[globk - ve[j].second] + ve[j].first);
}
}
}
for(int j = 0; j < ve.size(); ++j) {
if(ak[ve[j].second] == 0 || ak[ve[j].second] > ve[j].first) {
ak[ve[j].second] = ve[j].first;
}
}
}
}
while(vey.size()) {
ak[vey.top()] = 0;
vey.pop();
}
for(int i = 0; i < v[dg].size(); ++i) {
int x = v[dg][i].first;
if(!bo[x]) ama(cntr(x));
}
}
int best_path(int n, int k, int h[][2], int l[]) {
globk = k;
for(int i = 0; i < n; ++i) {
v[i].clear();
bo[i] = 0;
}
for(int i = 0; i < n - 1; ++i) {
v[h[i][0]].push_back({h[i][1], l[i]});
v[h[i][1]].push_back({h[i][0], l[i]});
}
ama(cntr());
return fp;
}
#ifdef wambule
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n = 11;
int k = 12;
int h[][2] = {0, 1, 0, 2, 2, 3, 3, 4, 4, 5, 0, 6, 6, 7, 6, 8, 8, 9, 8, 10};
int l[] = {3, 4, 5, 4, 6, 3, 2, 5, 6, 7};
int rtnd = best_path(n, k, h, l);
cout << "[fnps] " << rtnd << endl;
return 0;
}
#endif
