#include <bits/stdc++.h>
using namespace std;
/*
John Watson
https://codeforces.com/profile/quangminh98
Mua Code nhu mua Florentino !!
*/
#define faster() ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define ll long long
const int maxn = 2e5 + 9;
vector<int> adj[maxn];
int sz[maxn], par[20][maxn], h[maxn];
ll val[maxn], dist[maxn];
int n;
ll k;
void DFS(int u, int p = -1)
{
sz[u] = 1;
for (int v : adj[u])
{
if (v == p) continue;
h[v] = h[u] + 1;
par[0][v] = u;
for (int i = 1; i < 20; i++)
par[i][v] = par[i - 1][par[i - 1][v]];
DFS(v, u);
sz[u] += sz[v];
}
}
int LCA(int u, int v)
{
if (h[u] < h[v]) swap(u, v);
int k = h[u] - h[v];
for (int i = 0; i < 20; i++)
if (k >> i & 1)
u = par[i][u];
if (u == v) return u;
for (int i = 19; i >= 0; i--)
if (par[i][u] != par[i][v])
{
u = par[i][u];
v = par[i][v];
}
return par[0][u];
}
void DFS_compute(int u, int p = -1)
{
for (int v : adj[u])
{
if (v == p) continue;
dist[v] = dist[u] + val[v];
DFS_compute(v, u);
}
}
int best_path(int _n, int _k, int H[][2], int l[])
{
n = _n;
k = _k;
for (int i = 0; i < n - 1; i++)
{
int u = H[i][0], v = H[i][1];
u++; v++;
adj[u].push_back(v);
adj[v].push_back(u);
}
DFS(1);
for (int i = 0; i < n - 1; i++)
{
ll w = l[i];
int u = H[i][0], v = H[i][1];
u++; v++;
val[h[u] > h[v] ? u : v] = w;
}
DFS_compute(1);
int ans = 1e9;
for (int u = 1; u <= n; u++)
for (int v = u + 1; v <= n; v++)
{
int lca = LCA(u, v);
if (dist[v] + dist[u] - 2 * dist[lca] == k) ans = min(ans, h[u] + h[v] - 2 * h[lca]);
// cout << u - 1 << ' ' << v - 1 << ' ' << dist[v] + dist[u] - 2 * dist[lca] << '\n';
}
return (ans == 1e9 ? -1 : ans);
}
