#include<bits/stdc++.h>
// #define long long long long
#define fi first
#define se second
#define pb push_back
#define ii pair<long long, long long>
#define sz(v) (long long)v.size()
#define all(v) v.begin(), v.end()
using namespace std;
const long long N=2e5+5, mod = 1e9+7, inf = 1e18;
struct Edge {
long long to, w;
};
long long n, k;
vector<Edge> adj[N];
bool del[N];
long long sz[N], dist[10*N];
long long ans = inf;
void dfs(long long v, long long p=-1) {
sz[v] = 1;
for (auto [u, w]:adj[v]) {
if (u!=p && !del[u]) {
dfs(u, v);
sz[v]+=sz[u];
}
}
}
void dfs_ans(long long v, long long p=-1, long long sum=0, long long d=0) {
if (k<sum) return;
if (dist[k-sum]<inf) ans = min(ans, dist[k-sum]+d);
for (auto [u, w]:adj[v]) {
if (u!=p && !del[u]) dfs_ans(u, v, sum+w, d+1);
}
}
void upd(long long v, long long p=-1, long long sum=0, long long d=0) {
if (k<sum) return;
dist[sum] = min(dist[sum], d);
for (auto [u, w] : adj[v]) {
if (u!=p && !del[u]) upd(u, v, sum+w, d+1);
}
}
void init(long long v, long long p = -1, long long sum = 0) {
if (k<sum) return;
dist[sum] = inf;
for (auto [u, w] : adj[v]) {
if (u!=p && !del[u]) init(u, v, sum+w);
}
}
long long centroid(long long v, long long p, long long nn) {
for (auto [u, w] : adj[v]) {
if (u!=p && !del[u]) {
if (sz[u]*2>nn) return centroid(u, v, nn);
}
}
return v;
}
void solve(long long v) {
dfs(v);
dist[0] = 0;
for (auto [u, w] : adj[v]) {
if (!del[u]) {
dfs_ans(u, v, w, 1);
upd(u, v, w, 1);
}
}
init(v);
del[v] = 1;
for (auto [u, w] : adj[v]) {
if (!del[u]) solve(centroid(u, v, sz[u]));
}
}
int best_path(int N, int K, int H[][2], int L[]) {
n = N; k = K;
for (long long i=0; i<n-1; i++) {
long long u, v, w;
u = H[i][0]; v = H[i][1]; w = L[i];
adj[u].pb({v, w});
adj[v].pb({u, w});
}
for (long long i=0; i<=10*200005-1; i++) dist[i] = inf;
dfs(0);
solve(centroid(0, -1, sz[0]));
if (ans==inf) return -1;
return (int) ans;
}
