#include "race.h"
//#pragma GCC optimize("O3,unroll-loops,Ofast")
//#pragma GCC target("avx2,bmi,bmi2,popcnt,lzcnt")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#define MAX 200005
#define pb push_back
// #define mp make_pair
#define int long long
#define f first
#define s second
#define vi vector<int>
#define pii pair<int,int>
#define si set<int>
#define vpii vector<pair<int,int>>
const int mod = 1e9+7;
const int INF = 1e18;
// myMap.begin()->first : key
// myMap.begin()->second : value
int epow(int a,int b){int ans=1;while(b){if(b&1) ans*=a;a*=a;b>>=1;ans%=mod;a%=mod;}return ans%mod;}
int gcd(int a,int b) {if(a<b)swap(a,b);while(b){int tmp=b;b=a%b;a=tmp;}return a;}
int mul(int a,int b){return ((a%mod)*(b%mod))%mod;}
int sum(int a,int b){return ((a%mod)+(b%mod))%mod;}
typedef tree<pii,null_type,less<pii>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;
// typedef
// tree<int,null_type,less_equal<int>,rb_tree_tag,tree_order_statistics_node_update>ordered_multiset;
vpii adj[MAX];
int n,k,dep[MAX],dep2[MAX],ans=INF;
ordered_set st[MAX];
void dfs(int node,int par){
st[node].insert({dep[node],node});
for(auto u : adj[node]){
if(u.f==par) continue;
dep[u.f]=dep[node]+u.s; dep2[u.f]=dep2[node]+1;
dfs(u.f,node);
for(auto x : st[u.f]){
int need = k+2*dep[node]-x.f;
auto itr = st[node].upper_bound({need,-1});
// if(itr==st[node].end() || (*itr).f!=need) continue;
while(itr!=st[node].end() && (*itr).f==need) ans=min(ans, dep2[x.s]+dep2[(*itr).s]-2*dep2[node] ), itr++;
}
if(st[u.f].size()>st[node].size()) st[node].swap(st[u.f]);
for(auto x : st[u.f]) st[node].insert(x);
}
}
int best_path(int N, int K, int H[][2], int L[])
{
n=N; k=K;
for(int i=0;i<n-1;i++){
adj[H[i][0]].pb({H[i][1],L[i]}); adj[H[i][1]].pb({H[i][0],L[i]});
}
dfs(1,0);
cout<<((ans==INF)?-1:ans)<<endl;
if(ans==INF) ans=-1;
return ans;
}
