// #include "race.h"
#include<bits/stdc++.h>
#define fi first
#define se second
#define ull unsigned long long
#define ll long long
#define BIT(a , b) ((a >> b) & 1)
#define turnOn(a , b) ((a) | (1 << (b)))
#define turnOff(a , b) ((a) ^ (1 << (b)))
#define pii pair<ll , ll>
#define pb push_back
#define nl cout << "\n";
#define __ <<" "<<
#define mem(a, b) memset((a), (b), sizeof((a)))
#define all(c) (c).begin(), (c).end()
#define file "test"
using namespace std;
const int oo = 1e9 + 7;
const int mod = 1e9 + 7;
const int N = 2e5 + 5;
const int LOG = 20;
int n , child[N];
ll depth[N] , ans = oo;
ll k;
ll dist[N];
vector <pii> adj[N];
vector <int> vt[N];
map <ll , set<ll>> cnt;
void getsz(int i , int p){
child[i] = 1;
for(auto it : adj[i]){
int j = it.fi;
if(j == p) continue;
depth[j] = depth[i] + 1;
dist[j] = dist[i] + it.se;
getsz(j , i);
child[i] += child[j];
}
}
void sack(int i , int p , bool keep){
int best_node = -1;
int Max = -1;
for(auto it : adj[i]){
int j = it.fi;
if(j == p) continue;
if(child[j] > Max){
Max = child[j];
best_node = j;
}
}
for(auto it : adj[i]){
int j = it.fi;
if(j != p && j != best_node) sack(j , i , 0);
}
if(best_node != -1){
sack(best_node , i , 1);
swap(vt[i] , vt[best_node]);
}
vt[i].pb(i);
// cout << i << ' ' << cnt[dist[i] + k].size() << ' ' << dist[i] + k << ' ' << keep << '\n';
if(cnt[dist[i] + k].size()){
// cout << "ff\n";
ans = min(ans , *cnt[dist[i] + k].begin() - depth[i]);
}
cnt[dist[i]].insert(depth[i]);
// cout << i << ' ' << dist[i] << ":\n";
for(auto it : adj[i]){
int j = it.fi;
if(j == p || j == best_node) continue;
for(auto x : vt[j]){
ll tmp = k - (dist[x] - dist[i]) + dist[i];
// cout << dist[x] << ' ' << dist[i] << ' ' << tmp << '\n';
if(cnt[tmp].size()){
// cout << i << ' ' << x << ' ' << tmp << '\n';
ans = min(ans , depth[x] + *cnt[tmp].begin() - 2 * depth[i]);
}
}
for(auto x : vt[j]){
cnt[dist[x]].insert(depth[x]);
vt[i].pb(x);
}
}
// cout << i << ' ' << keep << ":\n";
// for(auto j : vt[i]) cout << j << ' ';
// nl;
if(!keep){
for(auto x : vt[i]){
cnt[dist[x]].erase(depth[x]);
// cout << x << '/' << cnt[dist[x]].size() << ' ';
}
// nl;
}
}
int best_path(int _N, int _K, int _H[][2], int _L[])
{
// if(_K == 1) return 0;
n = _N;
k = _K;
for(int i = 0 ; i < n - 1 ; i++){
int u , v , w;
u = _H[i][0];
v = _H[i][1];
w = _L[i];
u++;
v++;
adj[u].pb({v , w});
adj[v].pb({u , w});
}
getsz(1 , 0);
sack(1 , 0 , 0);
if(ans != oo) return ans;
else return -1;
}
// void run_with_file(){
// if(fopen(file".inp","r")){
// freopen(file".inp","r", stdin);
// freopen(file".out", "w", stdout);
// }
// }
// int main(){
// run_with_file();
// cin >> n >> k;
// for(int i = 0 ; i < n - 1 ; i++){
// int u , v , w;
// cin >> u >> v >> w;
// u++;
// v++;
// adj[u].pb({v , w});
// adj[v].pb({u , w});
// }
// getsz(1 , 0);
// sack(1 , 0 , 0);
// if(ans != oo) cout << ans;
// else cout << -1;
// }
/* UwU */
