#include <bits/stdc++.h>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#define MAX_N 500000
int N, K;
int HH[MAX_N][2];
int LL[MAX_N];
using namespace std;
typedef int ll;
vector <pair <ll, ll> > ND[200005];
ll A[200005];
queue <pair <ll, ll> > Q;
ll P, PV;
vector <pair <ll, ll> > NG;
ll find_mp(ll k, ll pk, ll n){
vector <pair <ll, ll> > PG;
ll m=0, s=0;
for (ll i=0; i<ND[k].size(); i++) {
ll nk = ND[k][i].first;
if (pk == nk or A[nk]) continue;
ll v = find_mp(nk, k, n);
m = max(m, v);
s += v;
PG.push_back({nk, v});
}
if(pk!=-1){
m = max(m, n-s-1);
PG.push_back({pk, n-s-1});
}
//cout<<k<<" "<<s<<" "<<m<<"\n";
if (PV>m) {
PV = m;
P = k;
NG = move(PG);
}
return s+1;
}
ll M[1000005];
ll rez = INT_MAX;
vector <pair<ll,ll> > V;
void path(ll id, ll pid, ll v, ll d){
if(v>K) return;
//cout<<id<<" "<<v<<" "<<d<<"\n" ;
V.push_back({v,d});
if(M[K-v]!=INT_MAX) rez = min(rez, M[K-v]+d);
for(ll i=0; i<ND[id].size(); i++){
ll nid = ND[id][i].first;
ll nv = ND[id][i].second;
if(pid == nid or A[nid]) continue;
path(nid, id, v+nv, d+1);
}
}
int best_path(int n, int k, int H[][2], int L[]) {
N=n;
K=k;
for(ll i=0;i<n-1;i++){
ND[H[i][0]].push_back({H[i][1], L[i]});
ND[H[i][1]].push_back({H[i][0], L[i]});
}
Q.push({0, n});
while (!Q.empty()){
PV=INT_MAX;
ll sz = Q.front().second;
find_mp(Q.front().first, -1, sz);
Q.pop();
A[P] = 1;
for (ll i=0; i<NG.size(); i++){
if(NG[i].second>1)Q.push({NG[i].first, NG[i].second});
}
//cout<<P<<"\n";
for(ll i=0; i<=K; i++){
M[i] = INT_MAX;
}
M[0]=0;
for(ll i=0; i<ND[P].size(); i++){
ll ni = ND[P][i].first;
ll nv = ND[P][i].second;
//cout<<"hello\n";
path(ni, -1, nv, 1);
for(ll j=0; j<V.size(); j++) M[V[j].first]=min(M[V[j].first], V[j].second);
V.clear();
}
//for(ll i=0;i<=K;i++) cout<<(M[i]==INT_MAX?-1:M[i])<<" "; cout<<"\n";
//cout<<rez<<"\n__________\n";
}
return rez==INT_MAX?-1:rez;
}
/*int main()
{
//freopen("in.txt", "r", stdin);
ifstream cin("in.in");
cin>>N>>K;
for(ll i=0;i<N-1;i++){
cin>>HH[i][0]>>HH[i][1]>>LL[i];
}
ll ans = best_path(N, K, HH, LL);
cout<<ans;
}*/
