#include <bits/stdc++.h>
using namespace std;
#define ll long long int
const int N = 2e5 + 1;
int n, k, max_depth;
int sz[N];
bool vis[N];
vector<pair<int, int>> adj[N];
int res = INT_MAX;
map<int, int> cnt;
int get_subtree_size(int u, int p)
{
sz[u] = 1;
for (auto [v, w] : adj[u])
{
if (v != p and !vis[v])
sz[u] += get_subtree_size(v, u);
}
return sz[u];
}
int get_centroid(int u, int p, int tree_size)
{
for (auto [v, w] : adj[u])
{
if (v != p and !vis[v] and (sz[v] * 2 > tree_size))
return get_centroid(v, u, tree_size);
}
return u;
}
void calc(int u, int p, int fill, int weight, int depth = 1)
{
if (fill == 1)
{
if (cnt.count(weight))
{
cnt[weight] = min(cnt[weight], depth);
}
else
{
cnt[weight] = depth;
}
}
else if ((weight <= k) and (cnt.count(k - weight)))
{
res = min(res, depth + cnt[k - weight]);
}
for (auto [v, w] : adj[u])
{
if (!vis[v] and (v != p))
calc(v, u, fill, weight + w, depth + 1);
}
}
void decompose(int u, int p)
{
int tree_size = get_subtree_size(u, p);
int centroid = get_centroid(u, p, tree_size);
vis[centroid] = true;
cnt.clear();
cnt[0] = 0;
for (auto [v, w] : adj[centroid])
{
if (!vis[v] and v != p)
calc(v, centroid, 0, w), calc(v, centroid, 1, w);
}
for (auto [v, w] : adj[centroid])
{
if (!vis[v] and v != p)
decompose(v, centroid);
}
}
int best_path(int N, int K, int edges[][2], int weight[2])
{
n = N;
k = K;
for (int i = 0; i < n - 1; ++i)
{
int u, v, w;
u = edges[i][0];
v = edges[i][1];
w = weight[i];
adj[u].push_back({v, w});
adj[v].push_back({u, w});
}
decompose(0, -1);
if (res == INT_MAX)
return -1;
return res;
}
