#include <bits/stdc++.h>
#define mp make_pair
#define pb push_back
using namespace std;
const int MN = 200010;
int n,k,ans,sz[MN],dead[MN];
vector<pair<int,int> > g[MN];
void get_sz(int cur,int prev){
sz[cur] = 1;
for(auto &x : g[cur]) if(x.first!=prev && !dead[x.first]){
get_sz(x.first,cur);
sz[cur] += sz[x.first];
}
}
int dfs(int cur,int prev,int tot){
for(auto &x : g[cur]) if(x.first!=prev && !dead[x.first]){
if(sz[x.first]>(tot/2)) return dfs(x.first,cur,tot);
}
return cur;
}
int one(int root){
get_sz(root,-1);
return dfs(root,-1,sz[root]);
}
void rec(int start){
int c = one(start);
dead[c] = 1;
for(auto &x : g[c]) if(!dead[x.first]) rec(x.first);
map<int,int> cnt;
function<void (int,int,int,int,int)> add_cnt = [&](int cur,int prev,int d,int st,int add){
if(d>k) return;
cnt[d] = cnt[d]?min(cnt[d],st):st;
for(auto &x : g[cur]) if(x.first!=prev && !dead[x.first]){
add_cnt(x.first,cur,d+x.second,st+1,add);
}
};
function<void (int,int,int,int)> calc = [&](int cur,int prev,int d,int st){
if(d>k) return;
if(k!=d && cnt[k-d]) ans = min(ans,st+cnt[k-d]);
for(auto &x: g[cur]) if(x.first!=prev && !dead[x.first]){
calc(x.first,cur,d+x.second,st+1);
}
};
add_cnt(c,-1,0,0,1);
if(cnt[k]) ans = min(ans,cnt[k]);
cnt.clear();
for(auto &x : g[c]) if(!dead[x.first]){
calc(x.first,c,x.second,1);
add_cnt(x.first,c,x.second,1,1);
}
dead[c] = 0;
}
int best_path(int _n,int _k,int h[][2],int l[]){
ans = MN;
n = _n; k = _k;
for(int i=0;i<n-1;i++){
int a = h[i][0];
int b = h[i][1];
int c = l[i];
g[a].pb(mp(b,c));
g[b].pb(mp(a,c));
}
rec(0);
if(ans>=MN) ans = -1;
return ans;
}
