#include <bits/stdc++.h>
using namespace std;
#define all(x) x.begin(),x.end()
long long ask(const std::vector<int> &w);
void answer(int s, int t);
void find_pair(int N, std::vector<int> U, std::vector<int> V, int A, int B) {
vector<vector<pair<int,int>>> adj(N);
for(int i=0;i<U.size();i++){
adj[U[i]].emplace_back(V[i],i);
adj[V[i]].emplace_back(U[i],i);
}
vector<int> pedge(N);
vector<int> depth(N);
function<void(int,int,int,int)> dfs = [&](int x,int p,int dep,int par){
depth[x]=dep;
pedge[x]=par;
for(auto&i:adj[x])if(i.first!=p)dfs(i.first,x,dep+1,i.second);
};
dfs(0,-1,0,-1);
int M = U.size();
auto base = ask(vector<int>(M));
auto basedep = base/((long long)A);
// Calculate st
vector<pair<int,int>> arr;
for(int i=0;i<N;i++)arr.emplace_back(depth[i],i);
sort(arr.rbegin(),arr.rend());
auto check = [&](int x){
vector<int> wt(M);
for(int i=0;i<x;i++)wt[pedge[arr[i].second]]=1;
return base==ask(wt);
};
int st = 0;
for(int jump = 65536;jump;jump/=2){
if(st+jump>=N)continue;
if(check(st+jump))st+=jump;
}
st = arr[st].second;
dfs(st,-1,0,-1);
vector<int> sus;
for(int i=0;i<N;i++)if(depth[i]==basedep)sus.emplace_back(i);
while(sus.size()>1){
int mid = (sus.size())/2;
vector<int> left,right;
for(int i=0;i<mid;i++)left.emplace_back(sus[i]);
for(int i=mid;i<sus.size();i++)right.emplace_back(sus[i]);
vector<int> w(M);
for(int&i:left)w[pedge[i]]=1;
auto ans = ask(w);
if(ans!=base)sus=left;
else sus=right;
}
answer(st, sus[0]);
}
