#include <bits/stdc++.h>
#include "highway.h"
//#include "grader.cpp"
using namespace std;
#define ll long long
int n;
vector <pair <int, int> > es, g[90001];
ll light;
int find(int root){
vector <bool> vis(n);
queue <int> ready;
vector <int> depth(n);
ready.push(root);
vector <int> edges;
while(ready.size()){
int node = ready.front();
vis[node] = 1;
ready.pop();
for(auto &i : g[node]){
if(vis[i.first]) continue;
depth[i.first] = depth[node] + 1;
edges.push_back(i.second);
ready.push(i.first);
}
}
reverse(edges.begin(), edges.end());
int l = 0, r = n - 1;
while(l <= r){
int mid = (l + r) / 2;
vector <int> check(n - 1);
for(int i = 0 ; i <= mid ; i++){
check[edges[i]] = 1;
}
if(ask(check) != light) r = mid - 1;
else l = mid + 1;
}
auto edge = es[edges[l]];
if(depth[edge.first] > depth[edge.second]) return edge.first;
return edge.second;
}
void find_pair(int N, std::vector<int> u, std::vector<int> v, int a, int b) {
n = N;
for(int i = 0 ; i < n - 1 ; i++){
g[u[i]].push_back(make_pair(v[i], i));
g[v[i]].push_back(make_pair(u[i], i));
es.push_back(make_pair(u[i], v[i]));
}
light = ask(vector <int>(n - 1, 0));
int s = find(0);
int t = find(s);
answer(s, t);
}
