#include <iostream>
#include <vector>
#include <cmath>
#include <numeric>
#include <algorithm>
#include <set>
#include <unordered_set>
#include <cstring>
#include <unordered_map>
#include <iomanip>
#include <queue>
#include <map>
#include <sstream>
#include <stack>
#include <bitset>
using ll = long long;
using ld = long double;
using namespace std;
const int nm = 200002;
const ll inf = 1e18;
vector<pair<int, ll>> adj[nm];
int H[nm][2], L[nm];
int Res;
bool deleted[nm];
void bfs(int i, int n, int k) {
// cout << "bfs " << i << " " << n << " " << k << "\n";
queue<int> q;
q.push(i);
vector<pair<ll, ll>> d(n, {inf, inf});
d[i] = {0, 0};
while (q.size()) {
int i = q.front();
q.pop();
for (auto [j, w]: adj[i]) {
if (deleted[j]) continue;
if (d[j].second > d[i].second + 1) {
d[j].first = d[i].first + w;
d[j].second = d[i].second + 1;
if (d[j].second < Res && d[j].first < k) q.push(j);
}
}
}
unordered_map<ll, int> best;
for (int j = 0; j < n; ++j) {
if (d[j].first == inf) continue;
if (d[j].first == k) Res = min(Res, (int) d[j].second);
else if (best.count(k - d[j].first)) {
Res = min(Res, (int) d[j].second + best[k - d[j].first]);
}
if (best.count(d[j].first)) best[d[j].first] = min(best[d[j].first], (int) d[j].second);
else best[d[j].first] = d[j].second;
}
}
void dfs(int i, int p, vector<int> &nchild, vector<int> &maxchild) {
nchild[i] = 1;
for (auto [j, w]: adj[i]) {
if (j == p || deleted[j]) continue;
dfs(j, i, nchild, maxchild);
nchild[i] += nchild[j];
maxchild[i] = max(maxchild[i], nchild[j]);
}
}
int findCenter(int root, int n) {
vector<int> nchild(n), maxchild(n);
dfs(root, -1, nchild, maxchild);
int s = nchild[root];
if (s == 1) return -1;
for (int i = 0; i < n; ++i) {
if (nchild[i] > 0) {
int maxsplit = max(maxchild[i], s - nchild[i]);
if (maxsplit <= s / 2) return i;
}
}
return -1;
}
void calc(int root, int n, int k) {
int u = findCenter(root, n);
// cout << "root " << root << " center " << u << "\n";
if (u == -1) return;
bfs(u, n, k);
// cout << "root " << root << " center " << u << " " << Res << "\n";
deleted[u] = 1;
for (auto [j, w]: adj[u]) {
if (!deleted[j]) calc(j, n, k);
}
}
int best_path(int n, int k, int H[][2], int L[]) {
for (int i = 0; i < n - 1; ++i) {
adj[H[i][0]].emplace_back(H[i][1], L[i]);
adj[H[i][1]].emplace_back(H[i][0], L[i]);
}
memset(deleted, 0, sizeof(deleted));
Res = n + 1;
calc(0, n, k);
return Res < n ? Res : -1;
}
// int main() {
// #ifdef LOCAL
// freopen("input.txt", "r", stdin);
// #endif
// ios::sync_with_stdio(0);
// cin.tie(0);
// int n, k;
// cin >> n >> k;
// for (int i = 0; i < n - 1; ++i) cin >> H[i][0] >> H[i][1] >> L[i];
// cout << best_path(n, k, H, L) << "\n";
// }
