#include <bits/stdc++.h>
#define name "vestonluvto"
const char* namein = name ".inp";
const char* nameout = name ".out";
#define fastio() ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define PI 3.141592653589793238462
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define pb emplace_back
using namespace std;
#ifndef LOCAL
#define debug(x) cerr << #x <<" "; _print(x); cerr << endl;
#else
#define debug(x)
#endif
void _print(int t) {cerr << t;}
void _print(long long t) {cerr << t;}
void _print(string t) {cerr << t;}
void _print(char t) {cerr << t;}
void _print(long double t) {cerr << t;}
void _print(double t) {cerr << t;}
void _print(unsigned long long t) {cerr << t;}
template <class T, class V> void _print(pair <T, V> p);
template <class T> void _print(vector <T> v);
template <class T> void _print(set <T> v);
template <class T, class V> void _print(map <T, V> v);
template <class T> void _print(multiset <T> v);
template <class T, class V> void _print(pair <T, V> p) {cerr << "{"; _print(p.first); cerr << ","; _print(p.second); cerr << "}";}
template <class T> void _print(vector <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(set <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(multiset <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void _print(map <T, V> v) {cerr << "[ "; for (auto i : v) {_print(i); cerr << " ";} cerr << "]";}
void homefix(){
#ifndef LOCAL
freopen("fixcode.txt", "w", stderr);
#endif
}
void home(){
homefix();
if (fopen(namein, "r")) {
freopen(namein, "r", stdin);
freopen(nameout, "w", stdout);
}
}
const int MAXN = 2e5 + 5;
int n;
long long k;
vector<pair<long long, int > > dt[MAXN];
void nhap(){
cin >> n >> k;
for(int i = 1; i < n; i++){
int u, v;
long long w;
cin >> u >> v >> w;
u++;
v++;
dt[u].pb(w, v);
dt[v].pb(w, u);
}
}
int depth[MAXN], sz[MAXN];
int arr[MAXN], tin[MAXN], tout[MAXN], id;
long long t[MAXN];
vector<long long> vt;
void prpdfs(int u, int p){
sz[u] = 1;
vt.pb(t[u]);
arr[++id] = u;
tin[u] = id;
depth[u] = depth[p] + 1;
for(auto &[w, v] : dt[u])if(v != p){
t[v] = t[u] + w;
prpdfs(v, u);
sz[u] += sz[v];
}
tout[u] = id;
}
map<long long, int> luu;
void bfsolve(){
prpdfs(1, 0);
}
int kq = 1e9;
void sack(int u, int p, bool keep){
int big = 0;
for(auto &[w, v] : dt[u]) if(v != p && sz[v] > sz[big]) big = v;
for(auto &[w, v] : dt[u]) if(v != p && v != big) sack(v, u, 0);
if(big != 0) sack(big, u, 1);
long long kk = (long long)k + t[u];
if(luu.count(kk)){
kq = min(kq, luu[kk] - depth[u]);
}
if(!luu.count(t[u])) luu[t[u]] = depth[u];
else luu[t[u]] = min(luu[t[u]], depth[u]);
for(auto &[w, v] : dt[u]) if(v != p && v != big){
for(int idx = tin[v]; idx <= tout[v]; idx++){
int x = arr[idx];
long long kkk = k + 2LL * t[u] - t[x];
if(luu.count(kkk)){
kq = min(kq, luu[kkk] + depth[x] - 2*depth[u]);
}
}
for(int idx = tin[v]; idx <= tout[v]; idx++){
int x = arr[idx];
if(!luu.count(t[x])) luu[t[x]] = depth[x];
else luu[t[x]] = min(luu[t[x]], depth[x]);
}
}
if(!keep){
for(int idx = tin[u]; idx <= tout[u]; idx++){
int v = arr[idx];
luu.erase(t[v]);
}
}
}
void solve(){bfsolve();
sack(1, 0, 1);
if(kq > 1e6)cout << -1;
else cout << kq;
}
int main(){
fastio(); home();int t = 1;
//cin >> t;
while(t--)nhap(), solve();
return 0;
}
/* ___________
╔══╗ ▐▀▄ ▄▀▌ ▄▄▄▄▄▄▄ / \
╚╗╔╝ ▌▒▒▀▄▄▄▄▄▀▒▒▐▄▀▀▒██▒██▒▀▀ / MEO \
╔╝(¯’v´¯) ▐▒▒▒▒▀▒▀▒▀▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▀▄ \
╚══’.¸. ▌▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▄▒▒▒▒▒▒▒▒▒▒▒▒▀▄ \ __________ /
╔♫═╗╔╗ kitten ▀█▒▒▒█▌▒▒█▒▒▐█▒▒▒▀▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▌ |/
╚╗╔╝║║♫═╦╦╦╔╗ ▀▌▒▒▒▒▒▒▀▒▀▒▒▒▒▒▒▀▀▒▒▒▒▒▒▒▒▒▒▒▒▒▒▐ ▄▄
╔╝╚╗♫╚╣║║║║╔╣ ▐▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▌▄█▒█
╚═♫╝╚═╩═╩♫╩═╝ ▐▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒█▒█▀
┊ ┊ ┊ ┊ ▐▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒█▀
┊ ┊ ┊ ┊ ▐▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▌
┊ ┊ ┊ ★ ▌▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▐
┊ ┊ ☆ ▐▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▌
┊ ★ ▌▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▐
☆ ▐▄▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▄▌
▀▄▄▀▀▀▀▀▄▄▀▀▀▀▀▀▀▄▄▀▀▀▀▀▄▄▀
*/
