#include <bits/stdc++.h>
using namespace std;
const int MAXN=2e5+1;
const int MAXK=1e6+1;
int n, k, u, v, w, sz[MAXN], dp[MAXK], ans=MAXN;
bool isCentroid[MAXN];
vector<array<int, 2> > a[MAXN];
unordered_set<int>W;
void DFS(int u, int p)
{
sz[u]=1;
for (auto it:a[u]){
int v=it[0];
if(v==p or isCentroid[v]) continue;
DFS(v, u);
sz[u]+=sz[v];
}
}
int findCentroid(int u, int p, int treeSz)
{
for (auto it:a[u]){
int v=it[0];
if(v!=p and !isCentroid[v] and sz[v]>treeSz/2){
return findCentroid(v, u, treeSz);
}
}
return u;
}
void calc(int u, int p, int h, int cur_w)
{
if(cur_w<=k){
if(dp[k-cur_w]!=MAXN) ans=min(ans, h+dp[k-cur_w]);
}
else return;
W.insert(cur_w);
for (auto it:a[u]){
int v=it[0], w=it[1];
if(v==p or isCentroid[v]) continue;
calc(v, u, h+1, cur_w+w);
}
}
void update(int u, int p, int h, int cur_w)
{
if(cur_w>k) return;
dp[cur_w]=min(dp[cur_w], h);
for (auto it:a[u]){
int v=it[0], w=it[1];
if(v==p or isCentroid[v]) continue;
update(v, u, h+1, cur_w+w);
}
}
void build(int u)
{
DFS(u, -1);
int centroid=findCentroid(u, -1, sz[u]);
isCentroid[centroid]=1;
dp[0]=0;
W.insert(0);
for (auto it:a[centroid]){
int v=it[0], w=it[1];
if(!isCentroid[v]){
calc(v, centroid, 1, w);
update(v, centroid, 1, w);
}
}
for (auto x:W) dp[x]=MAXN;
for (auto it:a[centroid]){
int v=it[0];
if(!isCentroid[v]){
build(v);
}
}
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
cin >> n >> k;
for (int i=1; i<n; i++){
cin >> u >> v >> w;
a[u].push_back({v, w});
a[v].push_back({u, w});
}
for (int i=0; i<=k; i++){
dp[i]=MAXN;
}
build(0);
if(ans==MAXN) cout << -1;
else cout << ans;
return 0;
}
