#include <bits/stdc++.h>
#define ll long long
#define pii pair<long long,long long>
using namespace std;
const ll maxn = 5e5 + 2;
ll sz[maxn],h[maxn],k;
vector<pii> a[maxn];
ll ans = LLONG_MAX;
map<ll,ll> mp[maxn];
void dfs(ll u, ll w, ll pa) {
assert(h[u]!=0);
for (pii tmp : a[u]) {
ll wv,v; tie(v,wv) = tmp;
if (v==pa) continue;
h[v] = h[u] + 1;
dfs(v,w+wv,u);
mp[v][w+wv] = h[v];
if (mp[u].size() < mp[v].size()) swap(mp[u],mp[v]);
for (pii val : mp[v]) {
if (val.second==0) continue;
if (val.first - w < k && mp[u][k-val.first+2*w] != 0) {
ans = min(ans, mp[u][k-val.first+2*w] - h[u] + val.second - h[u]);
}
}
for (pii val : mp[v]) {
if (val.second==0) continue;
mp[u][val.first] = mp[u][val.first] == 0 ? val.second : min(val.second,mp[u][val.first]);
}
if (mp[u][w + k] != 0) {
ans = min(ans, mp[u][w+k]-h[u]);
}
}
}
int best_path(int _n, int _k, int _h[][2], int _L[])
{
k = _k;
for (ll i = 0; i < _n - 1; i++){
ll x = _h[i][0], y = _h[i][1];
ll w = _L[i];
a[x].push_back({y,w});
a[y].push_back({x,w});
}
h[0] = 1;
dfs(0,0,-1);
assert(ans > 0);
return ans == LLONG_MAX ? -1 : ans;
}
//void file(string name) {
// if (fopen((name + ".inp").c_str(), "r")) {
// freopen((name + ".inp").c_str(), "r", stdin);
// freopen((name + ".out").c_str(), "w", stdout);
// }
//}
//signed main() {
// file("race");
// int N,K; cin >> N >> K;
// int h[N][2],l[N];
// for (int i = 0; i < N-1; i++) {
// int x,y,w; cin >> x >> y >> w;
// h[i][1] = x;
// h[i][0] = y;
// l[i] = w;
// }
// cout << best_path(N,K,h,l);
//}
