#include <bits/stdc++.h>
using namespace std;
#define ss second
#define ff first
typedef long long ll;
#define ll ll
using pi = array<ll, 2>;
const ll MOD = 1e9+7;
const int maxn = 2e5 + 1;
vector<pair<int,int>> 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.ff) { continue; }
precomp(n.ff, u, c + n.ss, h + 1);
}
}
void small_to_large_merge(int u, int p) {
ll target = K + 2 * sum[u];
for (auto n : adj[u]) {
if (n.ff == p) { continue; }
small_to_large_merge(n.ff, u);
if (info[n.ff].size() > info[u].size()) { swap(info[n.ff], info[u]); }
for (auto i : info[n.ff]) {
if (info[u].find(target - i.ff) != info[u].end()) {
ret = min(ret, info[u][target - i.ff] + i.ss - 2 * dist[u]);
}
}
for (auto i : info[n.ff]) {
if (info[u].find(i.ff) == info[u].end()) {
info[u].insert(i);
} else {
info[u][i.ff] = min(info[u][i.ff], i.ss);
}
}
}
}
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].push_back(pair<int,int>(v, weights[i]));
adj[v].push_back(pair<int,int>(u, weights[i]));
}
precomp(0, -1, 0, 0);
small_to_large_merge(0, -1);
return ret == INT_MAX ? -1 : ret;
}
