#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
#define endl "\n"
#define ll long long
#define IOS ios_base::sync_with_stdio(false); cin.tie(nullptr);
const int N = 2e5 + 5;
int sz[N];
bool seen_c[N];
int parent_c[N];
int depth[N];
long long path[N];
vector<pair<int, int>> adj[N];
map<long long, int> mp;
int ans = N;
void dfs_subtree(int u, int p) {
sz[u] = 1;
for (auto [v, wt] : adj[u]) {
if (v != p && !seen_c[v]) {
dfs_subtree(v, u);
sz[u] += sz[v];
}
}
return;
}
int dfs_centroid(int u, int p, int n) {
for (auto [v, wt] : adj[u]) {
if (v != p && !seen_c[v] && sz[v] > n / 2) {
return dfs_centroid(v, u, n);
}
}
return u;
}
void dfs1(int u, int p, int k) {
if (path[u] <= k) {
auto it = mp.find(k - path[u]);
if (it != mp.end()) {
ans = min(ans, depth[u] + it->second);
}
}
if (path[u] == k) {
ans = min(ans, depth[u]);
}
for (auto [v, wt] : adj[u]) {
if (v != p && !seen_c[v]) {
path[v] = path[u] + wt;
depth[v] = depth[u] + 1;
dfs1(v, u, k);
}
}
return;
}
void dfs2(int u, int p, int k) {
auto it = mp.find(path[u]);
if (it == mp.end()) {
mp[path[u]] = depth[u];
} else {
mp[path[u]] = min(mp[path[u]], depth[u]);
}
for (auto [v, wt] : adj[u]) {
if (v != p && !seen_c[v]) {
dfs2(v, u, k);
}
}
return;
}
void build(int u, int p, int k) {
dfs_subtree(u, u);
int c = dfs_centroid(u, u, sz[u]);
if (p == -1) {
p = c;
}
parent_c[c] = p;
seen_c[c] = true;
for (auto [v, wt] : adj[c]) {
if (!seen_c[v]) {
depth[v] = 1;
path[v] = wt;
dfs1(v, v, k);
dfs2(v, v, k);
}
}
mp.clear();
for (auto [v, wt] : adj[c]) {
if (!seen_c[v]) {
build(v, c, k);
}
}
return;
}
int main() {
IOS;
int n, k;
cin >> n >> k;
for (int i = 0; i < n - 1; i++) {
int u, v, wt;
cin >> u >> v >> wt;
adj[u].push_back(make_pair(v, wt));
adj[v].push_back(make_pair(u, wt));
}
build(0, -1, k);
if (ans == N) {
ans = -1;
}
cout << ans;
return 0;
}
