#include <bits/stdc++.h>
#include "race.h"
using namespace std;
const int N_ = 2e5+1;
vector<vector<pair<int,int>>> a;
map<int,int> mp[N_];
int n,k,len[N_],sum[N_],ans = 1e9;
void dfs(int pos,int last,int ln,int sm)
{
len[pos] = ln;
sum[pos] = sm;
mp[pos][sm] = ln;
for(auto x : a[pos])
{
if(x.first == last)continue;
dfs(x.first,pos,ln+1,sm+x.second);
}
return ;
}
void solve(int pos,int last)
{
int K = k + 2 * sum[pos];
for(auto v : a[pos])
{
if(v.first == last)continue;
solve(v.first,pos);
if(mp[v.first].size() > mp[pos].size())swap(mp[v.first],mp[pos]);
for(auto i : mp[v.first])
{
if(mp[pos].find(K-i.first) != mp[pos].end()){
ans = min(ans,mp[pos][K-i.first] + i.second - 2 * len[pos]);
}
}
for(auto i : mp[v.first]){
if(mp[pos].find(i.first) == mp[pos].end()){
mp[pos].insert(i);
}else{
mp[pos][i.first] = min(mp[pos][i.first],i.second);
}
}
}
}
int best_path(int n_, int k_, int h[][2], int l[])
{
n = n_;k = k_;
a.resize(n);
for(int i = 0;i < n-1;i++)
{
int x = h[i][0],y = h[i][1];
a[x].push_back({y,l[i]});
a[y].push_back({x,l[i]});
}
dfs(0,-1,0,0);
solve(0,-1);
if(ans == 1e9)return -1;
else return ans;
}
