#include "highway.h"
#include<bits/stdc++.h>
using namespace std;
int n;
vector<vector<int> > ar, id;
vector<int> marc, sub;
vector<int> nulo;
vector<int> ans;
long long iniVal;
void centDecomp(int cur, bool flag);
void preCalc(int cur, int pai);
int getCent(int cur, int pai, int tam);
void paint(int cur, int pai, vector<int>& w);
int bb(vector<int> values);
bool query(vector<int> w);
void find_pair(int N, std::vector<int> U, std::vector<int> V, int A, int B) {
n = N;
ar = id = vector<vector<int> > (n);
marc = sub = vector<int> (n);
nulo = vector<int> (U.size());
for(int i = 0; i < U.size(); i++){
ar[U[i]].push_back(V[i]);
ar[V[i]].push_back(U[i]);
id[U[i]].push_back(i);
id[V[i]].push_back(i);
}
iniVal = ask(nulo);
centDecomp(0, 1);
answer(ans[0], ans[1]);
}
void centDecomp(int cur, bool flag){
preCalc(cur, cur);
int cent = getCent(cur, cur, sub[cur]);
marc[cent] = 1;
vector<int> w = nulo;
vector<int> filhos;
for(int i = 0; i < ar[cent].size(); i++){
if(marc[ar[cent][i]]) continue;
w[id[cent][i]] = 1;
filhos.push_back(ar[cent][i]);
}
if(filhos.empty()) {
ans.push_back(cent);
return;
}
if(flag && query(w)){
int n1 = bb(filhos);
vector<int> filhos2;
for(int i = 0; i < filhos.size(); i++){
if(filhos[i] == n1) continue;
filhos2.push_back(filhos[i]);
}
int n2 = bb(filhos2);
if(n1 != -1)
centDecomp(n1, 0);
if(n2 != -1)
centDecomp(n2, 0);
if(n2 == -1 || n1 == -1)
ans.push_back(cent);
return;
}
int next = bb(filhos);
if(next == -1){
ans.push_back(cent);
return;
}
centDecomp(next, flag);
}
void preCalc(int cur, int pai){
sub[cur] = 1;
for(int i = 0; i < ar[cur].size(); i++){
int viz = ar[cur][i];
if(marc[viz] || viz == pai) continue;
preCalc(viz, cur);
sub[cur] += sub[viz];
}
}
int getCent(int cur, int pai, int tam){
for(int i = 0; i < ar[cur].size(); i++){
int viz = ar[cur][i];
if(marc[viz] || viz == pai|| sub[viz] <= tam / 2) continue;
return getCent(viz, cur, tam);
}
return cur;
}
void paint(int cur, int pai, vector<int>& w){
for(int i = 0; i < ar[cur].size(); i++){
int viz = ar[cur][i];
w[id[cur][i]] = 1;
if(marc[viz] || viz == pai) continue;
paint(viz, cur, w);
}
}
int bb(vector<int> values){
int ini = 0, fim = values.size() - 1;
vector<int> w = nulo;
for(int i = 0; i < values.size(); i++)
paint(values[i], values[i], w);
if(!query(w)) return -1;
while(ini != fim){
int mid = (ini + fim) >> 1;
vector<int> w = nulo;
for(int i = ini; i <= mid; i++)
paint(values[i], values[i], w);
if(query(w)) fim = mid;
else ini = mid + 1;
}
return values[ini];
}
bool query(vector<int> w){
return ask(w) != iniVal;
}
