#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
#ifndef LOCAL
#include "race.h"
#endif
const int N = 200'000 + 1;
int answer, wei;
vector<pair<int, int>> ad[N];
int tsz;
int sz[N];
bool mk[N];
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> node, undo;
int f[N], dis[N];
int d[1'000'010];
void dfs3(int u, int pre = -1) {
node.push_back(u);
for (const auto& [v, w] : ad[u]) {
if (v == pre) continue;
dis[v] = dis[u] + 1;
f[v] = f[u] + w;
dfs3(v, u);
}
undo.push_back(f[u]);
}
void clr() {
for (const auto& i : undo) d[i] = 1e7;
undo.clear();
}
void dfs4(int u, int pre = -1) {
dfs1(u, pre);
u = dfs2(u, pre);
mk[u] = true;
clr();
// cerr << u << " " << pre << "\n";
for (const auto& [v, w] : ad[u]) {
if (v == pre || mk[v]) continue;
node.clear();
f[v] = w; dis[v] = 1;
dfs3(v, u);
for (const auto& i : node) if (f[i] <= wei) {
answer = min(answer, dis[i] + d[wei - f[i]]);
// if (u == 1) cerr << i << " " << dis[i] << " " << d[wei - f[i]] << "\n";
}
for (const auto& i : node) if (f[i] <= wei) d[f[i]] = min(d[f[i]], dis[i]);
}
for (const auto& [v, w] : ad[u]) if (v != pre && !mk[v]) dfs4(v, u);
}
int best_path(int n, int k, int h[][2], int l[]) {
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});
}
answer = 1e7; wei = k;
memset(d, 40, sizeof d); d[0] = 0;
dfs4(0);
return answer > n ? -1 : answer;
}
#ifdef LOCAL
#define MAX_AA 500000
static int AA, K;
static int H[MAX_AA][2];
static int L[MAX_AA];
static int solution;
#define int long long
mt19937_64 rng(8384815663);
int rnd(int l, int r) { return l + rng() % (r - l + 1); }
inline
void my_assert(int e) {if (!e) abort();}
void read_input()
{
// AA = rnd(2e5, 2e5), K = rnd(100, 100);
cin >> AA >> K;
for (int i = 0; i < AA - 1; ++i) {
// H[i][0] = rnd(i, i);
// H[i][1] = i + 1;
// L[i] = rnd(1, 100);
cin >> H[i][0] >> H[i][1];
cin >> L[i];
}
solution = -1;
// cin >> solution;
}
int32_t main() {
int ans;
read_input();
ans = best_path(AA,K,H,L);
cout << ans << "\n";
return 0;
}
#endif
