#include <bits/stdc++.h>
using namespace std;
//#define lalala ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
//#define endl "\n"
//#define int long long int
#define N 200006
#define big 1000000000
#define p push
#define f first
#define s second
#define pb push_back
#define ins insert
int n,k;
vector<pair<int,int>> adj[N];
int sub[N];
int center[N];
int cev=big;
void dfs(int x,int baba){
sub[x]=1;
for(auto u:adj[x]){
if(u.f==baba||center[u.f]==1)continue;
dfs(u.f,x);
sub[x]+=sub[u.f];
}
}
int bul(int x,int hed,int once){
for(auto u:adj[x]){
if(center[u.f]||once==u.f)continue;
if(sub[u.f]>hed/2)return bul(u.f,hed,x);
}
return x;
}
vector<pair<int,int>> v;
void mes(int x,int once,int uzak,int kac){
if(uzak>k)return;
v.pb({uzak,kac});
for(auto u:adj[x]){
if(u.f==once||center[u.f])continue;
mes(u.f,x,uzak+u.s,kac+1);
}
}
void solve(int x){
dfs(x,-1);
int centroid=bul(x,sub[x],-1);
//cout<<centroid<<"_"<<endl;
center[centroid]=1;
set<pair<int,int>> yol;
yol.ins({0,0});
for(auto u:adj[centroid]){
if(center[u.f])continue;
v.clear();
mes(u.f,centroid,u.s,1);
for(auto u:v){
int deg=k-u.f;
auto uu=yol.lower_bound({deg,-1});
if(uu==yol.end())continue;
if((*uu).f==deg){
cev=min(cev,u.s+(*uu).s);
}
}
for(auto u:v){
yol.ins(u);
}
}
for(auto u:adj[centroid]){
if(center[u.f]==0){
solve(u.f);
}
}
}
int best_path(int nn, int kk, int h[][2], int l[]) {
n=nn;
k=kk;
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]});
}
solve(0);
if(cev==big)return -1;
return cev;
}
/*signed main(){
lalala;
int nn,kk;
cin>>nn>>kk;
int arr[nn][2],of[nn];
for(int i=0;i<nn-1;i++){
cin>>arr[i][0]>>arr[i][1];
}
for(int i=0;i<nn-1;i++){
cin>>of[i];
}
cout<<best_path(nn,kk,arr,of)<<endl;
}*/
