#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//using namespace __gnu_pbds;
using namespace std;
using ll=long long;
//typedef tree<int,null_type,less_equal<int>,rb_tree_tag, tree_order_statistics_node_update> ordered_set;
#define mem(a,x) memset(a,x,sizeof(a))
#define fast(s) s.reserve(2000); s.max_load_factor(0.5);
#define F first
#define S second
#define pii pair <int, int>
#define all(p) p.begin(), p.end()
template<typename T> bool maximum(T &A, const T &B) {return A<B? A=B, true: false;}
template<typename T> bool minimum(T &A, const T &B) {return A>B? A=B, true: false;}
const int mod=998244353;
const int base=2999;
const int INF=1e9;
const int N=2e5+2, LOG=30, M=1e6+5;
int n, k, cnt[N], mn[M];
ll res;
bool del[N];
vector<pii> e[N];
void file()
{
#define task "codeforces"
if(fopen(task".inp","r"))
{
freopen(task".inp","r",stdin);
freopen(task".out","w",stdout);
}
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
}
void Count(int u, int pre)
{
cnt[u]=1;
for(auto [v,_]: e[u])
{
if(v==pre || del[v]) continue;
Count(v,u);
cnt[u]+=cnt[v];
}
}
int centroid(int u, int pre, int n)
{
for(auto [v,_]: e[u])
{
if(v==pre || del[v]) continue;
if(cnt[v]>n/2) return centroid(v,u,n);
}
return u;
}
void DFS(int u, int pre, int d, int len)
{
if(d==k) minimum(res,(ll)len);
if(d>k) return;
minimum(res,(ll)len+mn[k-d]);
for(auto [v,w]: e[u])
{
if(v==pre || del[v]) continue;
DFS(v,u,d+w,len+1);
}
}
void update(int u, int pre, int d, int len, bool ok)
{
if(d>k) return;
if(ok) minimum(mn[d],len);
else mn[d]=INF;
for(auto [v,w]: e[u])
{
if(v==pre || del[v]) continue;
update(v,u,d+w,len+1,ok);
}
}
void calc(int u)
{
Count(u,0);
u=centroid(u,0,cnt[u]);
for(auto [v,w]: e[u])
{
if(del[v]) continue;
DFS(v,u,w,1);
update(v,u,w,1,1);
}
for(auto [v,w]: e[u])
{
if(del[v]) continue;
update(v,u,w,1,0);
}
del[u]=1;
for(auto [v,_]: e[u])
{
if(del[v]) continue;
calc(v);
}
}
void Solve()
{
cin>>n>>k;
for(int i=1; i<n; ++i)
{
int u, v, w; cin>>u>>v>>w;
e[u].push_back({v,w});
e[v].push_back({u,w});
}
res=INF;
fill(mn,mn+M,INF);
calc(0);
cout<<(res==INF? -1: res);
}
main()
{
file();
Solve();
return 0;
}
