#include "race.h"
#include <vector>
#include <map>
#include <iostream>
// #define IS_DEBUG
using namespace std;
typedef long long ll;
template<typename a, typename b> ostream& operator<< (std::ostream &out, const pair<a, b> &p) {
out << "(" << p.first << ", " << p.second << ")";
return out;
}
const bool DEBUG = false;
const int MAXN = 2e5 + 5;
ll _K, ans = MAXN, o1[MAXN], o2[MAXN];
vector< pair<ll, ll> > adj_list[MAXN];
map<ll, ll> paths[MAXN]; // length, num
void dfs(int cur, int p) {
for (auto &n : adj_list[cur]) {
ll neigh = n.first, l = n.second;
if (p == neigh) continue;
dfs(neigh, cur);
if (paths[neigh].size() > paths[cur].size()) {
paths[cur].swap(paths[neigh]);
o1[neigh] += l;
o2[neigh]++;
o1[cur] -= l;
o2[cur]--;
swap(o1[cur], o1[neigh]);
swap(o2[cur], o2[neigh]);
}
for (auto e : paths[neigh]) {
if (paths[cur].count(_K - (e.first + l + o1[neigh]) - o1[cur])) {
ans = min(ans, paths[cur][_K - (e.first + l + o1[neigh]) - o1[cur]] + e.second + 1 + o2[neigh] + o2[cur]);
if (DEBUG) cerr << cur << ": " << paths[cur][_K - (e.first + l + o1[neigh]) - o1[cur]] + e.second + 1 + o2[neigh] + o2[cur] << endl;
// only with newly added cuz from differnt subtrees
}
}
for (auto e : paths[neigh]) {
if (paths[cur].count(e.first + l + o1[neigh] - o1[cur])) {
paths[cur][e.first + l + o1[neigh] - o1[cur]] = min(paths[cur][e.first + l + o1[neigh] - o1[cur]], e.second + 1 + o2[neigh] - o2[cur]);
} else {
paths[cur][e.first + l + o1[neigh] - o1[cur]] = e.second + 1 + o2[neigh] - o2[cur];
}
}
paths[neigh].clear();
}
if (paths[cur].count(_K - o1[cur])) {
ans = min(ans, paths[cur][_K - o1[cur]] + o2[cur]);
if (DEBUG) cerr << cur << ": " << paths[cur][_K - o1[cur]] + o2[cur] << endl;
}
paths[cur][-o1[cur]] = -o2[cur];
if (DEBUG) {
cerr << cur << ": " << o1[cur] << " " << o2[cur] << " ";
for (auto e : paths[cur]) cerr << e << " ";
cerr << endl;
}
}
int best_path(int N, int K, int H[][2], int L[]) {
_K = K;
for (int i = 0; i < N - 1; i++) {
adj_list[H[i][0]].push_back({H[i][1], L[i]}), adj_list[H[i][1]].push_back({H[i][0], L[i]});
}
dfs(0, -1);
return (ans == MAXN) ? -1 : ans;
}
#ifdef IS_DEBUG
int main() {
int n, k;
cin >> n >> k;
int h[MAXN][2], l[MAXN];
for (int i = 0 ; i < n - 1; i++) {
cin >> h[i][0] >> h[i][1] >> l[i];
}
cout << best_path(n, k, h, l) << endl;
return 0;
}
#endif
