#include <bits/stdc++.h>
#define pb push_back
#define all(x) x.begin(), x.end()
#define F first
#define S second
#define con continue
using namespace std;
typedef long long ll;
typedef double db;
typedef long double ld;
typedef pair<ll,ll> pii;
const ll N = 1e5 + 5;
const ll MOD = 1e9 + 7;
const ll maxn = 6e5 + 5;
const ll inf = 1e9+1;
const ll INF = 1e18;
const ll K = 31;
/*vector <ll> z_function(string s){
// ll n = s.size();
// ll l = 0,r = 0;
// vector <ll> z(n);
// for(ll i = 1;i < n;i++){
// if(i <= r){
// z[i] = (r - i + 1,z[i - l]);
// }
// while(i + z[i] < n && s[z[i]] == s[z[i] + i]){
// z[i]++;
// }
// if(i + z[i] - 1 > r){
// r = i + z[i]-1;
// l = i;
// }
// }
}*/
/*vector <ll> prefix_function(string s){
ll n = s.size();
vector <ll> pi(n,0);
for(ll i = 1;i < n;i++){
ll j = pi[i - 1];
while(j > 0 && s[i] != s[j]){
j = pi[j - 1];
}
if(s[i] == s[j])++j;
pi[i] = j;
}
return pi;
}*/
vector <pii> g[N];
int d,ans = inf,C,was[N];
int get_sz(int v,int p,int n){
int sz= 1 ;
for(auto [to,w] : g[v]){
if(was[to] || to == p)con;
sz += get_sz(to,v,n);
}
if(!C && (sz+sz>=n || p == 0))C = v;
return sz;
}
set <int> has;
map<int,int> val;
int dep[N],dis[N];
void dfs(int v,int p){
if(has.count(d - dis[v]) == 1){
ans = min(ans,(dep[v]+val[(d - dis[v])]));
}
for(auto [to,w] : g[v]){
if(to == p || was[to])con;
dis[to] = dis[v] + w;
dep[to] = dep[v] + 1;
dfs(to,v);
}
}
void add(int v,int p){
if(has.count(dis[v]) == 0){
has.insert(dis[v]);
val[dis[v]] = dep[v];
}
val[dis[v]] = min(val[dis[v]],dep[v]);
for(auto [to,w] : g[v]){
if(was[to] || to == p)con;
add(to,v);
}
}
void centr_decop(int v,int n){
C = 0;
get_sz(v,0,n);
int c = C;
has.clear();
val.clear();
dis[c] = dep[c] = 0;
for(auto [to,w] : g[c]){
if(was[to])con;
dep[to] = dep[c] + 1;
dis[to] = dis[c] + w;
dfs(to,c);
add(to,c);
}
was[c] = 1;
for(auto [to,w] : g[c]){
if(was[to])con;
centr_decop(to,n / 2);
}
}
int best_path(int nn,int k,int h[][2],int l[]){
int n = nn+1;
d = k;
for(int i = 1;i < n;i++){
int u = h[i][0];
int v = h[i][1];
u++;
v++;
int w = l[i];
g[u].pb({v,w});
g[v].pb({u,w});
}
centr_decop(1,n);
if(ans == inf)return -1;
return ans;
}
//void solve(){
//}
//main(){
// ios_base::sync_with_stdio(0);
// cin.tie(0);
// ll abd = 1;
//// freopen("yinyang.in","r",stdin);
//// freopen("yinyang.out","w",stdout);
//
//// cin >> abd;
// for(ll i = 1;i <= abd;i++){
// solve();
// }
//}
