#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pi pair<int, int>
#define vi vector<int>
const int MAXN = 200005;
int n, k;
vector<pi> adj[MAXN];
bool processed[MAXN];
int sb_size[MAXN];
map<int, int> cnt;
int res = INT32_MAX;
int mx_depth = 0;
int get_sb_size(int v, int p) {
int res = 1;
for (pi e : adj[v]) {
int to, w;
tie(to, w) = e;
if (to == p || processed[to]) continue;
res += get_sb_size(to, v);
}
sb_size[v] = res;
return res;
}
int get_centroid(int v, int p, int s) {
for (pi e : adj[v]) {
int to, w;
tie(to, w) = e;
if (to == p || processed[to]) continue;
if (sb_size[to] > s / 2) return get_centroid(to, v, s);
}
return v;
}
void get_cnt(int v, int p, int depth, int s, bool fill) {
if (s > k) return;
// mx_depth = max(mx_depth, depth);
if (fill) {
// cerr << 1 << endl;
if (cnt.count(s)) cnt[s] = min(cnt[s], depth);
else cnt[s] = depth;
} else if (cnt.count(k - s)) {
// cerr << 1;
res = min(res, cnt[k - s] + depth);
}
for (pi e : adj[v]) {
int to, w;
tie(to, w) = e;
if (to == p || processed[to]) continue;
get_cnt(to, v, depth + 1, s + w, fill);
}
}
void centroid_decomp(int v, int p) {
int c = get_centroid(v, p, get_sb_size(v, p));
processed[c] = true;
// mx_depth = 0;
for (pi e : adj[c]) {
int to, w;
tie(to, w) = e;
if (processed[to]) continue;
get_cnt(to, c, 1, w, false);
get_cnt(to, c, 1, w, true);
}
cnt.clear();
cnt[0] = 0;
for (pi e : adj[c]) {
int to, w;
tie(to, w) = e;
if (to == p || processed[to]) continue;
centroid_decomp(to, c);
}
}
signed best_path(signed N, signed K, signed h[][2], signed l[]) {
n = N;
k = K;
for (int i = 0; i < n - 1; ++i) {
int a, b, w;
a = h[i][0];
b = h[i][1];
w = l[i];
// cerr << a << ' ' << b << ' ' << w << endl;
adj[a].push_back({b, w});
adj[b].push_back({a, w});
}
cnt[0] = 0;
centroid_decomp(0, -1);
if (res == INT32_MAX) res = -1;
return res;
}
signed main() {
signed a[][2] = {{0, 1}, {1, 2}, {1, 3}};
signed b[] = {1, 2, 4};
cout << best_path(4, 3, a, b);
}
