#include "race.h"
#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define ln '\n'
const int N = 2e5 + 5;
const int LG = 20;
const int INF = 0x3f3f3f3f;
const int MOD = 998244353;
int n, k;
int h[N][2], l[N];
int mn[N], sz[N], ans = INF, mx; // mn # that has length i
vector<pair<int, int>> adj[N];
bitset<N> removed;
void init(){
cin >> n >> k;
for (int i = 0; i < n-1; i++) cin >> h[i][0] >> h[i][1] >> l[i];
}
int get_size(int u, int p){
sz[u] = 1;
for (auto& [v, e]: adj[u]){
if (v == p || removed[v]) continue;
sz[u] += get_size(v, u);
}
return sz[u];
}
int get_centroid(int u, int p, int s){
for (auto& [v, e]: adj[u]){
if (v == p || removed[v]) continue;
if (sz[v] > s / 2) return get_centroid(v, u, s);
}
return u;
}
void dfs(int u, int p, int dep, int cur_len, int m){
if (cur_len > k) return;
mx = max(mx, dep);
if (m == 1) {ans = min(ans, dep + mn[k-cur_len]);}
else mn[cur_len] = min(mn[cur_len], dep);
for (auto& [v, e]: adj[u]){
if (v == p || removed[v]) continue;
dfs(v, u, dep+1, cur_len + e, m);
}
}
void build(int u){
int c = get_centroid(u, -1, get_size(u, -1));
removed[c] = 1;
mx = 0;
for (auto& [v, e]: adj[c]){
if (removed[v]) continue;
dfs(v, c, 1, e, 1);
dfs(v, c, 1, e, 0);
}
for (int i = 1; i <= mx; i++) mn[i] = INF;
for (auto& [v, e]: adj[c]){
if (removed[v]) continue;
build(v);
}
}
void init(int N, int K, int H[][2], int L[]){
// cin >> n >> k;
// for (int i = 0; i < n-1; i++) cin >> h[i][0] >> h[i][1] >> l[i];
n = N;
k = K;
for (int i = 0; i < n-1; i++){
h[i][0] = H[i][0];
h[i][1] = H[i][1];
l[i] = L[i];
}
}
int solve(){
for (int i = 0; i < n-1; i++){
adj[h[i][0]].push_back({h[i][1], l[i]});
adj[h[i][1]].push_back({h[i][0], l[i]});
}
memset(mn, 0x3f, sizeof(mn));
mn[0] = 0;
build(1);
return ((ans == INF)? -1: ans);
}
int best_path(int N, int K, int H[][2], int L[])
{
init(n, k, h, l);
return solve();
}
