#include <bits/stdc++.h>
//#include "race.h"
#define ll long long
#define pii pair<ll, ll>
#define fi first
#define se second
#define pb push_back
using namespace std;
const ll MX=200007, INF=1e9+7;
ll N, K, ret=INF;
map<ll, ll> ada[MX];
vector<pii> adj[MX];
pii lazy[MX];
void DFS(int par, int idx){
lazy[idx]={0, 0};
ada[idx][0]=0;
for(auto i:adj[idx]){
int v=i.fi, w=i.se;
if(v==par)
continue;
DFS(idx, v);
lazy[v].fi+=w;
lazy[v].se++;
if(ada[idx].size()<ada[v].size()){
swap(ada[idx], ada[v]);
swap(lazy[idx], lazy[v]);
}
for(auto jj:ada[v]){
pii j=jj;
j.fi+=lazy[v].fi-lazy[idx].fi;
j.se+=lazy[v].se-lazy[idx].se;
if(ada[idx].count(K-j.fi-lazy[idx].fi*2))
ret=min(ret, lazy[idx].se*2+j.se+ada[idx][K-j.fi-lazy[idx].fi*2]);
}
for(auto jj:ada[v]){
pii j=jj;
j.fi+=lazy[v].fi-lazy[idx].fi;
j.se+=lazy[v].se-lazy[idx].se;
if(ada[idx].count(j.fi))
ada[idx][j.fi]=min(ada[idx][j.fi], j.se);
else
ada[idx][j.fi]=j.se;
}
}
if(ada[idx].count(K-lazy[idx].fi))
ret=min(ret, lazy[idx].se+ada[idx][K-lazy[idx].fi]);
}
int best_path(int n, int k, int H[][2], int L[]){
N=n, K=k;
for(int i=0, u, v, w; i<N-1; i++){
u=H[i][0], v=H[i][1], w=L[i];
adj[u].pb({v, w});
adj[v].pb({u, w});
}
DFS(0, 0);
return (ret>=INF?-1:ret);
}
