#include <bits/stdc++.h>
using namespace std;
#define el "\n"
#define FOR(i,a,b) for(int i = (a), _b = (b); i <= _b; i++)
#define FORD(i,a,b) for(int i = (a), _b = (b); i >= _b; i--)
#define pb push_back
#define fi first
#define se second
#define all(x) x.begin(),x.end()
#define lg(x) __lg(x)
#define alla(a,n) a+1,a+n+1
#define ll long long
template <class T> bool maxi(T &x, T y) { if(x < y) { x = y ; return true ;} return false;}
template <class T> bool mini(T &x, T y) { if(x > y) { x = y ; return true ;} return false;}
const int N = 1e6 + 2;
const int maxT = 1e6 + 2;
int n, L;
vector<pair<int, int>> adj[N];
void inp()
{
cin >> n >> L;
FOR(i, 1, n - 1) {
int x, y, w; cin >> x >> y >> w;
x++; y++;
adj[x].pb({y, w});
adj[y].pb({x, w});
}
}
/* Try your best
No regrets */
namespace subtask_1
{
#define pii pair<int, int>
bool vis[N];
int sz[N];
void dfs_sz(int u, int p)
{
sz[u] = 1;
for(pii x : adj[u]) {
int v = x.fi, w = x.se;
if(v == p || vis[v]) continue;
dfs_sz(v, u);
sz[u] += sz[v];
}
}
int centroid(int u, int p, int n)
{
for(pii x : adj[u]) {
int v = x.fi;
if(v == p || vis[v]) continue;
if(sz[v] > n / 2) return centroid(v, u, n);
}
return u;
}
int minDist[maxT];
int ans = -1;
void dfsAns(int u, int p, int depth, int dis)
{
if(dis <= L ){
if(minDist[L - dis] != -1) mini(ans, depth + minDist[L - dis]);
}
for(pii x : adj[u]) {
int v = x.fi, w = x.se;
if(v == p || vis[v]) continue;
dfsAns(v, u, depth + 1, dis + w);
}
}
void dfsUpd(int u, int p, int depth, int dis)
{
if(dis <= L) {
if(minDist[dis] == -1) minDist[dis] = depth;
else mini(minDist[dis], depth);
}
for(pii x : adj[u]) {
int v = x.fi, w = x.se;
if(v == p || vis[v]) continue;
dfsUpd(v, u, depth + 1, dis + w);
}
}
void dfsReset(int u, int p, int depth, int dis)
{
if(dis <= L) {
minDist[dis] = -1;
}
for(pii x : adj[u]) {
int v = x.fi, w = x.se;
if(v == p || vis[v]) continue;
dfsReset(v, u, depth + 1, dis + w);
}
}
void Calc(int u)
{
vis[u] = 1;
dfs_sz(u, 0);
minDist[0] = 0;
for(pii x : adj[u]) {
int v = x.fi, w = x.se;
if(vis[v]) continue;
dfsAns(v, u, 1, w);
dfsUpd(v, u, 1, w);
}
minDist[0] = -1;
for(pii x : adj[u]) {
int v = x.fi, w = x.se;
if(vis[v]) continue;
dfsReset(v, u, 1, w);
}
for(pii x : adj[u]) {
int v = x.fi;
if(vis[v]) continue;
Calc(centroid(v, u, sz[v]));
}
}
void slv()
{
if(!L ){
cout << 0; return;
}
FOR(i, 1, L) minDist[i] = -1;
ans = n + 1;
dfs_sz(1, 0);
Calc(centroid(1, 0, n));
cout << (ans == n + 1 ? -1 : ans);
}
}
/* Code slowly, think carefully */
main()
{
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define __Azul__ "race"
if(fopen(__Azul__".inp", "r")) {
freopen(__Azul__".inp", "r", stdin);
freopen(__Azul__".out", "w", stdout);
}
bool qs = 0;
int T = 1;
if(qs) cin >> T;
while(T--) {
inp();
subtask_1::slv();
}
cerr << "\nTime" << 0.001 * clock() << "s "; return 0;
}
