#include "race.h"
#include<bits/stdc++.h>
using namespace std;
vector< pair<int,int> > edg[200005];
int k;
bool solved[200005];
int compsize[200005];
int mxdeg, centroid;
vector< pair<long long, int> > v;
set< pair<long long, int> > v2;
int ans = 1e9;
void findcentroid(int x, int p) {
compsize[x] = 1;
for(auto i:edg[x]) {
if(!solved[i.first] && i.first!=p) {
findcentroid(i.first, x);
compsize[x] += compsize[i.first];
}
}
}
void findcentroid2(int x, int p, int totsize) {
for(auto i:edg[x]) {
if(!solved[i.first] && i.first!=p) {
findcentroid2(i.first, x, totsize);
}
}
bool ok = true;
for(auto i:edg[x]) {
if(!solved[i.first] && i.first!=p) {
if(compsize[i.first] > totsize/2) ok = false;
}
}
if(totsize - compsize[x] > totsize/2) ok = false;
if(ok) centroid = x;
}
void solve(int x);
void findandsolve(int x) {
mxdeg = -1;
centroid = -1;
findcentroid(x, -1);
findcentroid2(x, -1, compsize[x]);
solve(centroid);
}
void dfs(int x, int p, long long len, int cnt) {
v.push_back({len, cnt});
for(auto i:edg[x]) {
if(solved[i.first]) continue;
if(i.first != p) {
dfs(i.first, x, len+i.second, cnt+1);
}
}
}
void solve(int x) {
v.clear(); v2.clear();
v2.insert({0, 0});
solved[x] = true;
for(auto i:edg[x]) {
if(solved[i.first]) continue;
v.clear();
dfs(i.first, -1, i.second, 1);
sort(v.begin(), v.end());
for(auto i:v) {
auto tmp = v2.lower_bound(make_pair(k-i.first, 0));
if(tmp!=v2.end() && (*tmp).first == k-i.first) {
ans = min(ans, (*tmp).second + i.second);
}
}
for(auto i:v) {
v2.insert(i);
}
}
for(auto i:edg[x]) {
if(solved[i.first]) continue;
findandsolve(i.first);
}
}
int best_path(int N, int K, int H[][2], int L[])
{
k = K;
for(int i=0; i<N-1; i++) {
edg[H[i][0]].push_back({H[i][1], L[i]});
edg[H[i][1]].push_back({H[i][0], L[i]});
}
compsize[0] = N;
findandsolve(0);
if(ans==1e9) return -1;
return ans;
}
