#include "race.h"
//#include "grader.cpp"
#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int maxn = 100100;
ll jmp[maxn][25], dis[maxn], depth[maxn], subtree[maxn], par[maxn];
int answ, KK, cnt[maxn];
set<pair<ll,ll>> adj[maxn];
map<pair<int,int>,int> M;
void dfs(int s, int p, int ok){
subtree[s]=1;
if(ok){
depth[s] = (p==-1?0:depth[p]+1);
dis[s] = (p==-1?0:dis[p]+M[{p,s}]);
jmp[s][0] = p;
}
for(auto x : adj[s]){
int u = x.first;
if(u==p) continue;
dfs(u,s,ok), subtree[s]+=subtree[u];
}
}
void dfs2(int s, int p, int dep, int weight, bool ok){
for(auto w : adj[s]){
int u = w.first;
if(u==p) continue;
dfs2(u,s,dep+1,weight+M[{s,u}],0);
dfs2(u,s,dep+1,weight+M[{s,u}],1);
}
int D = weight;
if(KK-D>=0 and !ok) answ = min(answ, dep+cnt[KK-D]);
if(ok) cnt[D] = min(cnt[D], dep);
}
int find_centroid(int s, int p, int sz){
for(auto u : adj[s])
if(u.first!=p and subtree[u.first]>sz/2)
return find_centroid(u.first, s, sz);
return s;
}
void centroid_decomp(int s, int p){
dfs(s,-1,0); int sz = subtree[s];
int centroid = find_centroid(s,-1,sz);
dfs2(centroid,p,0,0,0);
while(!adj[centroid].empty()){
int x = adj[centroid].begin()->first;
adj[x].erase(adj[x].lower_bound({centroid,-1}));
adj[centroid].erase(adj[centroid].begin());
centroid_decomp(x,centroid);
}
}
int best_path(int N, int K, int H[][2], int L[])
{
answ = N+1; KK = K; cnt[0]=0;
for(int i = 1; i <= K; i++) cnt[i]=N+1;
for(int i = 0; i < N-1; i++)
adj[++H[i][0]].insert({++H[i][1],L[i]}),
adj[H[i][1]].insert({H[i][0],L[i]}),
M[{H[i][0],H[i][1]}]=M[{H[i][1],H[i][0]}]=L[i];
dfs(1,-1,1), centroid_decomp(1,-1);
return (answ==N+1?-1:answ);
}
