//#include "race.h"
#include<bits/stdc++.h>
using namespace std;
const int M=2e5+5;
long long ans=INT_MAX;
vector<pair<int,int>>v[M];
#define pb push_back
#define ll long long
#define ff first
#define ss second
int sum[M],dst[M];
map<ll,ll> info[M];
int k;
void dfs(int a, int p, int h, ll d){
info[a][d]=h;
dst[a]=h;
sum[a]=d;
info[a][d]=h;
for(auto b:v[a]){
if(b.ff==p)continue;
dfs(b.ff,a,h+1,d+b.ss);
}
}
void fun(int a, int p){
ll t=k+2*sum[a];
for(auto b:v[a]){
if(b.ff==p)continue;
fun(b.ff,a);
if(info[b.ff].size()>info[a].size())swap(info[b.ff],info[a]);
for(auto i:info[b.ff]){
if(info[a].find(t-i.ff)!=info[a].end()){
ans=min(ans,info[a][t-i.ff]+i.ss-2*dst[a]);
}
}
for (auto i : info[b.ff]) {
if (info[a].find(i.ff) == info[a].end()) {
info[a].insert(i);
} else {
info[a][i.ff] = min(info[a][i.ff], i.ss);
}
}
}
}
int best_path(int N, int K, int H[][2], int L[]){
k=K;
if(k==1)return 0;
for(int i=0;i<N-1;i++){
int a=H[i][0];
int b=H[i][1];
int c=L[i];
v[a].pb({b,c});
v[b].pb({a,c});
}
dfs(0,-1,0,0);
fun(0,-1);
return ans==INT_MAX ? -1 : ans;
}
