#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pii;
#define pb push_back
#define f first
#define s second
const int maxn = 2e5 + 1;
vector<pii> adj[maxn];
map<ll, ll> info[maxn];
ll dist[maxn], sum[maxn];
int N, K;
ll ret;
void precomp(int u, int p, ll c, int h) {
info[u][c] = h;
sum[u] = c;
dist[u] = h;
for (auto n : adj[u]) {
if (p == n.f) {
continue;
}
precomp(n.f, u, c + n.s, h + 1);
}
}
void small_to_large_merge(int u, int p) {
ll target = K + 2 * sum[u];
for (auto n : adj[u]) {
if (n.f == p) {
continue;
}
small_to_large_merge(n.f, u);
if (info[n.f].size() > info[u].size()) { swap(info[n.f], info[u]); }
for (auto i : info[n.f]) {
if (info[u].find(target - i.f) != info[u].end()) {
ret = min(ret, info[u][target - i.f] + i.s - 2 * dist[u]);
}
}
for (auto i : info[n.f]) {
if (info[u].find(i.f) == info[u].end()) {
info[u].insert(i);
} else {
info[u][i.f] = min(info[u][i.f], i.s);
}
}
}
}
int best_path(int n, int k, int edges[][2], int weights[]) {
if (k == 1) {
return 0;
}
N = n;
K = k;
ret = INT_MAX;
for (int i = 0; i < n - 1; i++) {
int u = edges[i][0];
int v = edges[i][1];
adj[u].pb(pii(v, weights[i]));
adj[v].pb(pii(u, weights[i]));
}
precomp(0, -1, 0, 0);
small_to_large_merge(0, -1);
return ret == INT_MAX ? -1 : ret;
}
