#include <bits/stdc++.h>
#include "race.h"
using namespace std;
const int maxn=2e5;
vector<pair<long long,int>> adj[maxn];
int ans,dp[maxn],sz[maxn],k;
map<long long,int> m[maxn];
long long ds[maxn];
void dfs1(int v,int p){
for(auto[u,w]:adj[v])if(u!=p){
dp[u]=dp[v]+1;
ds[u]=ds[v]+w;
dfs1(u,v);
}
}
void dfs2(int v,int p){
int x=-1;
for(auto[u,w]:adj[v])if(u!=p){
if(x==-1||sz[u]>sz[x])x=u;
}
if(x!=-1){
dfs2(x,v);
swap(m[v],m[x]);
for(auto[u,w]:adj[v])if(u!=p&&u!=x){
dfs2(u,v);
for(auto[x,y]:m[u]){
if(m[v].count(k+2*ds[v]-x))ans=min(ans,m[v][k+2*ds[v]-x]+y-2*dp[v]);
}
for(auto[x,y]:m[u]){
if(!m[v].count(x))m[v][x]=y;
m[v][x]=min(m[v][x],y);
}
}
}
if(m[v].count(k+ds[v]))ans=min(ans,m[v][k+ds[v]]-dp[v]);
if(!m[v].count(ds[v]))m[v][ds[v]]=dp[v];
m[v][ds[v]]=min(m[v][ds[v]],dp[v]);
}
int best_path(int n, int K, int h[][2], int l[])
{
k=K;
for(int i=0;i<n-1;i++){
adj[h[i][0]].push_back({h[i][1],l[i]});
adj[h[i][1]].push_back({h[i][0],l[i]});
}
ans=1e9;
dfs1(0,0);
dfs2(0,0);
if(ans==1e9)ans=-1;
return ans;
}
