#ifndef yugi
#include "race.h"
#endif // yugi
#define maxn 200005
#define maxk 1000006
#include<bits/stdc++.h>
using namespace std;
int n, k, sz[maxn], del[maxn], mi[maxk];
vector <int> rollback;
vector <pair<int, int>> a[maxn];
void dfs(int u, int p) {
sz[u] = 1;
for (auto [v, w] : a[u]) if (v != p && !del[v]) dfs(v, u), sz[u] += sz[v];
}
int centroid(int u, int p, int cnt) {
for (auto [v, w] : a[u]) if (v != p && !del[v] && sz[v] * 2 > cnt) return centroid(v, u, cnt);
return u;
}
int ans = 1e9;
void query(int u, int p, int d, int len, int op) {
if (len > k) return;
if (op == 0) ans = min(ans, d + mi[k - len]);
else {
mi[len] = min(mi[len], d);
rollback.push_back(len);
}
for (auto [v, w] : a[u]) if (v != p && !del[v])
query(v, u, d+1, len+w, op);
}
void CentroidDecomposition(int u) {
dfs(u, -1);
int cen = centroid(u, -1, sz[u]);
del[cen] = 1;
mi[0] = 0;
for (auto [v, w] : a[cen]) if (!del[v]) {
query(v, cen, 1, w, 0);
query(v, cen, 1, w, 1);
}
for (int x:rollback) mi[x] = 1e9;
rollback.clear();
for (auto [v, w] : a[cen]) if (!del[v])
CentroidDecomposition(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++)
{
int u = H[i][0], v = H[i][1], w = L[i];
a[u].push_back({v, w});
a[v].push_back({u, w});
}
for (int i=1; i<=1e6; i++) mi[i] = 1e9;
CentroidDecomposition(0);
if (ans > n) ans = -1;
return ans;
}
#ifdef yugi
main() {
int n, k; cin >> n >> k;
int h[n+1][2], l[n+1];
for (int i=0; i<n-1; i++) {
cin >> h[i][0] >> h[i][1] >> l[i];
}
cout << best_path(n, k, h, l);
}
#endif // yugi
