#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int MX = 200001;
vector<pair<int, int>> adj[MX];
map<ll, int> m[MX];
ll distToRoot[MX], edgesToRoot[MX];
ll K;
ll ans = 1E9;
void dfs(int node, int prev)
{
m[node][distToRoot[node]] = node;
for (auto& [u, dist] : adj[node])
if (u != prev)
{
distToRoot[u] = distToRoot[node] + dist;
edgesToRoot[u] = edgesToRoot[node] + 1;
dfs(u, node);
if (m[node].size() < m[u].size())
swap(m[node], m[u]);
for (auto& [len, v] : m[u])
{
ll x = K - len + 2 * distToRoot[node];
if (m[node].count(x))
ans = min(ans, edgesToRoot[v] + edgesToRoot[m[node][x]] - 2 * edgesToRoot[node]);
}
for (auto& [len, v] : m[u])
{
if (m[node].count(len))
m[node][len] = edgesToRoot[m[node][len]] < edgesToRoot[v] ? m[node][len] : v;
else
m[node][len] = v;
}
}
}
int best_path(int N, int k, int H[][2], int L[])
{
K = k;
for (int i = 0; i < N - 1; ++i)
{
adj[H[i][0]].push_back({H[i][1], L[i]});
adj[H[i][1]].push_back({H[i][0], L[i]});
}
dfs(0, 0);
return ans == 1E9 ? -1 : ans;
}
