#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define F first
#define S second
#define pb push_back
#define pii pair<int, int>
const int maxN = 2e5 + 5;
const int maxW = 1e6 + 5;
const int inf = 1e9;
int n, sz[maxN], k;
vector<pii> g[maxN];
int edges[maxN][2], len[maxN];
int h[maxN], d[maxN];
int best[maxW];
int del[maxN];
int res = inf;
void count_child(int u, int p) {
sz[u] = 1;
for (pii it : g[u]) {
int v = it.F;
int w = it.S;
if (v == p || del[v]) continue;
count_child(v, u);
sz[u] += sz[v];
}
}
int find_centroid(int u, int p, int n) {
for (pii it : g[u]) {
int v = it.F;
int w = it.S;
if (v == p || del[v]) continue;
if (sz[v] > n / 2) return find_centroid(v, u, n);
}
return u;
}
void update(int u, int p, bool sta) {
if (sta == 0) {
if (d[u] == k) res = min(res, h[u]);
if (d[u] < k) {
if (best[k - d[u]] != 0) res = min(res, best[k - d[u]] + h[u]);
}
}
else {
if (d[u] <= k) {
if (best[d[u]] == 0) best[d[u]] = h[u];
else best[d[u]] = min(best[d[u]], h[u]);
}
}
for (pii it : g[u]) {
int v = it.F;
int w = it.S;
if (v == p || del[v]) continue;
h[v] = h[u] + 1;
d[v] = d[u] + w;
update(v, u, sta);
}
}
void delAns(int u, int p) {
if (d[u] <= k) best[d[u]] = 0;
for (pii it : g[u]) {
int v = it.F;
int w = it.S;
if (v == p || del[v]) continue;
delAns(v, u);
}
}
void solve(int u) {
count_child(u, 0);
int n = sz[u];
int root = find_centroid(u, 0, n);
del[root] = 1;
for (pii it : g[root]) {
int v = it.F;
int w = it.S;
if (del[v]) continue;
h[v] = 1;
d[v] = w;
update(v, root, 0);
update(v, root, 1);
}
d[root] = 0;
delAns(root, 0);
for (pii it : g[root]) {
int v = it.F;
int w = it.S;
if (del[v]) continue;
solve(v);
}
}
int best_path(int N, int K, int H[][2], int L[]) {
n = N;
k = K;
for (int i = 0; i < n - 1; i++) {
H[i][0]++;
H[i][1]++;
g[H[i][0]].pb({H[i][1], L[i]});
g[H[i][1]].pb({H[i][0], L[i]});
}
solve(1);
if (res == inf) return -1;
return res;
}
//signed main() {
// ios_base::sync_with_stdio(0);
// cin.tie(0);
// cin >> n >> k;
// for (int i = 0; i < n - 1; i++) {
// cin >> edges[i][0] >> edges[i][1] >> len[i];
// }
// cout << best_path(n, k, edges, len);
//}
