#ifndef LAK
#include <race.h>
#endif // LAK
#include <bits/stdc++.h>
#define no "NO"
#define yes "YES"
#define F first
#define S second
#define vec vector
#define task "main"
#define ll long long
#define _mp make_pair
#define ii pair<int, int>
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define evoid(val) return void(std::cout << val)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FOD(i, b, a) for(int i = (b); i >= (a); --i)
#define unq(x) sort(all(x)); x.resize(unique(all(x)) - x.begin())
using namespace std;
template<typename U, typename V> bool maximize(U &a, V b) {
if (a < b) { a = b; return 1; } return 0;
}
template<typename U, typename V> bool minimize(U &a, V b) {
if (a > b) { a = b; return 1; } return 0;
}
const int N = (int)2e5 + 9;
const int INF = (int)1e9;
const int MOD = (int)1e9 + 7;
int numNode, numDist;
vector<ii> adj[N];
int child[N], minEdge[(int)1e6 + 5];
bool del[N];
int ans = INF;
int countChild(int u, int p) {
child[u] = 1;
for (auto [v, w] : adj[u]) {
if (v == p || del[v]) continue;
countChild(v, u);
child[u] += child[v];
}
return child[u];
}
int centroid(int u, int p, int m) {
for (auto [v, w] : adj[u]) {
if (v == p || del[v]) continue;
if (child[v] > m / 2) return centroid(v, u, m);
}
return u;
}
void DFS_calc(int u, int p, int depth, int curLen) {
if (curLen > numDist) return;
minimize(ans, depth + minEdge[numDist - curLen]);
for (auto [v, w] : adj[u]) {
if (del[v] || v == p) continue;
DFS_calc(v, u, depth + 1, curLen + w);
}
}
void DFS_minimize(int u, int p, int depth, int curLen, vector<int> &tmp) {
if (curLen > numDist) return;
tmp.push_back(curLen);
minimize(minEdge[curLen], depth);
for (auto [v, w] : adj[u]) {
if (del[v] || v == p) continue;
DFS_minimize(v, u, depth + 1, curLen + w, tmp);
}
}
void cd(int u) {
int m = countChild(u, 0);
u = centroid(u, 0, m);
vector<int> tmp;
for (auto [v, w] : adj[u]) {
if (del[v]) continue;
DFS_calc(v, u, 1, w);
DFS_minimize(v, u, 1, w, tmp);
}
del[u] = 1;
for (int len : tmp) minEdge[len] = INF;
for (auto [v, w] : adj[u]) {
if (del[v]) continue;
cd(v);
}
}
int best_path(int n, int k, int h[][2], int l[]) {
numNode = n;
numDist = k;
FOR(i, 0, numNode - 2) {
int u = h[i][0], v = h[i][1];
int w = l[i];
u++;
v++;
adj[u].push_back({v, w});
adj[v].push_back({u, w});
}
FOR(i, 1, (int)1e6) minEdge[i] = INF;
cd(1);
return (ans != INF ? ans : -1);
}
#ifdef LAK
int edge[N][2];
int length[N];
void main_code() {
int numNode, requireDist;
cin >> numNode >> requireDist;
FOR(i, 0, numNode - 2) {
int u, v, l;
cin >> u >> v >> l;
edge[i][0] = u, edge[i][1] = v;
length[i] = l;
}
cout << best_path(numNode, requireDist, edge, length);
}
int main() {
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
if (fopen(task".inp", "r")) {
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
const bool MULTITEST = 0;
int num_test = 1; if (MULTITEST) cin >> num_test;
while (num_test--) { main_code(); cout << "\n"; }
}
#endif // LAK
/* Lak lu theo dieu nhac */
