#include "highway.h"
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define dbg(x) cerr << #x << ": " << x << "\n";
vector<pair<int, int>> depth;
vector<vector<pair<int, int>>> arr;
void dfs(int node, int prev = -1){
for(const auto &i : arr[node]){
if(i.first == prev) continue;
depth[i.first] = {depth[node].first + 1, i.second};
dfs(i.first, node);
}
}
int max_depht(int a, int b){
if(depth[a].first > depth[b].first) return a;
return b;
}
void find_pair(int N, std::vector<int> U, std::vector<int> V, int A, int B) {
depth.assign(N, {0, 0});
arr.assign(N, vector<pair<int, int>>());
vector<int> pos_ans;
vector<int> vec(U.size(), 0);
long long dis = ask(vec);
for(int i = 0; i < (int)U.size(); i++){
arr[U[i]].push_back({V[i], i});
arr[V[i]].push_back({U[i], i});
}
dfs(0);
for(const auto &i : depth){
if(i.first == dis / (long long)A){
pos_ans.push_back(i.second);
}
}
int l = 0, r = pos_ans.size();
while(l + 1 < r){
int m = (r + l) / 2;
for(int i = l; i < m; i++){
vec[pos_ans[i]] = 1;
}
long long aux = ask(vec);
vec.assign(U.size(), 0);
if(aux != dis){
r = m;
continue;
}
l = m;
}
answer(0, max_depht(U[pos_ans[l]], V[pos_ans[l]]));
}
