#include <bits/stdc++.h>
#define ll long long
#define pi pair<ll, ll>
#define fi first
#define se second
#define sz(x) (int)(x.size())
using namespace std;
const int Nmax = 2e5 + 55;
const ll inf = 1e17;
int N, dist[Nmax];
ll sum[Nmax], K, bestWay = inf;
map<ll, ll> info[Nmax];
vector<pi> edges[Nmax];
void dfs(int u, int par, ll curSum, int deep)
{
dist[u] = deep;
sum[u] = curSum;
info[u][curSum] = deep;
for(auto [r, v] : edges[u])
{
if (v != par)
{
dfs(v, u, curSum + r, deep + 1);
}
}
}
void merge_small_to_large(int u, int par)
{
ll target = K + 2 * sum[u];
for(auto [r, v] : edges[u])
{
if (v != par)
{
merge_small_to_large(v, u);
if (sz(info[u]) < sz(info[v])) swap(info[u], info[v]);
for(auto x : info[v])
{
if (info[u].find(target - x.fi) != info[u].end())
{
bestWay = min(bestWay, info[u][target - x.fi] + x.se - 2 * dist[u]);
}
}
for(auto x : info[v])
{
if (info[u].find(x.fi) == info[u].end())
{
info[u][x.fi] = x.se;
} else
{
info[u][x.fi] = min(info[u][x.fi], x.se);
}
}
}
}
}
int best_path(int n, int k, int H[][2], int L[])
{
N = n, K = k;
for(int i=0; i<n-1; i++)
{
edges[H[i][0]].push_back({L[i], H[i][1]});
edges[H[i][1]].push_back({L[i], H[i][0]});
}
dfs(0, n + 1, 0, 0);
merge_small_to_large(0, n + 1);
return (bestWay == inf ? -1 : bestWay);
}
