#include "highway.h"
#include <bits/stdc++.h>
#define ios ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define file(s) if (fopen(s".in", "r")) freopen(s".in", "r", stdin), freopen(s".out", "w", stdout)
#define all(a) a.begin() , a.end()
#define F first
#define S second
using namespace std;
using ll = long long;
const ll N = 2e5+5 , inf = 2e9 + 7;
const ll INF = 1e18 , mod = 1e9+7;
int dep[N] , road[N];
vector<pair<int,int>> g[N];
void dfs(int v, int p , int cost){
for(auto x : g[v]){
int to = x.S;
if(to != p) {
road[to] = x.F;
dep[to] = dep[v]+cost;
dfs(to,v,cost);
}
}
}
void find_pair(int n, vector<int> U, vector<int> V, int A, int B) {
vector<int> w;
for(int i = 0; i < U.size(); i++){
g[U[i]].push_back({i,V[i]});
g[V[i]].push_back({i,U[i]});
w.push_back(0);
}
vector<int> vec;
dfs(0,-1,A);
int cost1 = ask(w);
for(int i = 0; i < n; i++){
if(cost1 == dep[i]){
vec.push_back(i);
}
}
int l = 0 , r = vec.size()-1;
while(l <= r){
if(l == r){
answer(0,vec[l]);
return;
}
int md = (l+r) >> 1;
for(int i : vec) {
if(i <= md){
w[road[i]] = 0;
} else {
w[road[i]] = 1;
}
}
int cost = ask(w);
if(cost != cost1){
l = md+1;
} else {
r = md;
}
}
answer(0, N - 1);
}
