#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
#ifndef LOCAL
#include "race.h"
#endif
const int N = 200'000 + 1;
int n, k;
int answer = 1e7;
vector<pair<int, int>> ad[N];
int tsz;
int sz[N];
bool mk[N];
int cnt;
void dfs1(int u, int pre = -1) {
sz[u] = 1;
for (const auto& [v, w] : ad[u]) {
if (v == pre || mk[v]) continue;
dfs1(v, u);
sz[u] += sz[v];
}
tsz = sz[u];
}
int dfs2(int u, int pre = -1) {
for (const auto& [v, w] : ad[u]) {
if (v == pre || mk[v]) continue;
if (sz[v] > tsz / 2) return dfs2(v, u);
}
return u;
}
vector<int> undo;
vector<pair<int, int>> lst;
int d[1'000'010];
void dfs3(int u, int pre, int dis, int wei) {
lst.push_back({dis, wei});
undo.push_back(wei);
for (const auto& [v, w] : ad[u])
if (v != pre && !mk[v]) dfs3(v, u, dis + 1, wei + w);
}
void dfs4(int u, int pre = -1) {
dfs1(u, pre);
mk[u = dfs2(u, pre)] = true;
for (const auto& i : undo) if (i <= k) d[i] = 1e7;
d[0] = 0;
undo.clear();
for (const auto& [v, w] : ad[u]) {
if (v == pre || mk[v]) continue;
lst.clear(); dfs3(v, u, 1, w);
for (const auto& [dis, wei] : lst) if (wei <= k) answer = min(answer, dis + d[k - wei]);
for (const auto& [dis, wei] : lst) if (wei <= k) d[wei] = min(d[wei], dis);
}
for (const auto& [v, w] : ad[u]) if (v != pre && !mk[v]) dfs4(v, u);
}
int best_path(int a, int b, int h[][2], int l[]) {
n = a; k = b;
for (int i = 0; i < n - 1; ++i) {
int u = h[i][0], v = h[i][1], w = l[i];
ad[u].push_back({v, w});
ad[v].push_back({u, w});
}
memset(d, 40, sizeof d);
dfs4(0);
return answer > n ? -1 : answer;
}
#ifdef LOCAL
int h[N][2], l[N];
int32_t main() {
cin.tie(0)->sync_with_stdio(0);
cin >> n >> k;
for (int i = 0; i < n - 1; ++i) {
cin >> h[i][0] >> h[i][1];
cin >> l[i];
}
cout << best_path(n, k, h, l) << "\n";
}
#endif
