#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x, y) ((x + y - 1) / (y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
#define rep(i, n) for(int i = 0; i < n; ++i)
#define rep1(i, n) for(int i = 1; i <= n; ++i)
#define rev(i, s, e) for(int i = s; i >= e; --i)
#define trav(i, a) for(auto &i : a)
template<typename T>
void amin(T &a, T b) {
a = min(a, b);
}
template<typename T>
void amax(T &a, T b) {
a = max(a, b);
}
#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif
/*
refs:
http://www.algonotes.com/en/solutions-ioi2018/
edi
find an edge that lies on at least one sp from s to t
if edge is (u,v), then d(s,u)+d(u,t) = sp
can find s using bfs tree of u
once s found, t can also be found
*/
const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
#include "highway.h"
vector<pii> adj[N];
void find_pair(int n, std::vector<int> U, std::vector<int> V, int A, int B) {
int m = sz(U);
vector<pii> edges;
rep(i,m){
int u = U[i], v = V[i];
edges.pb({u,v});
adj[u].pb({v,i}), adj[v].pb({u,i});
}
// find an edge that lies on at least one sp from s to t
int all_light = -1;
{
vector<int> w(m);
all_light = ask(w);
}
int lo = 0, hi = m-1;
int first = -1;
while(lo <= hi){
int mid = (lo+hi) >> 1;
vector<int> w(m);
rep(i,mid+1){
w[i] = 1;
}
auto res = ask(w);
if(res != all_light){
first = mid;
hi = mid-1;
}
else{
lo = mid+1;
}
}
assert(first != -1);
// bfs tree of r
int r = edges[first].ff;
queue<int> q;
vector<int> dis(n,-1);
q.push(r);
dis[r] = 0;
vector<int> ord;
while(!q.empty()){
int u = q.front();
q.pop();
for(auto [v,id] : adj[u]){
if(dis[v] != -1) conts;
q.push(v);
dis[v] = dis[u]+1;
ord.pb(id);
}
}
// find s
lo = 0, hi = sz(ord)-1;
first = -1;
while(lo <= hi){
int mid = (lo+hi) >> 1;
vector<int> w(m,1);
rep(i,mid+1){
w[ord[i]] = 0;
}
auto res = ask(w);
if(res == all_light){
first = mid;
hi = mid-1;
}
else{
lo = mid+1;
}
}
assert(first != -1);
int s = -1;
{
auto [u,v] = edges[ord[first]];
if(dis[u] > dis[v]) s = u;
else s = v;
}
// bfs tree of s
fill(all(dis),-1);
q.push(s);
dis[s] = 0;
ord.clear();
while(!q.empty()){
int u = q.front();
q.pop();
for(auto [v,id] : adj[u]){
if(dis[v] != -1) conts;
q.push(v);
dis[v] = dis[u]+1;
ord.pb(id);
}
}
// find t
lo = 0, hi = sz(ord)-1;
first = -1;
while(lo <= hi){
int mid = (lo+hi) >> 1;
vector<int> w(m,1);
rep(i,mid+1){
w[ord[i]] = 0;
}
auto res = ask(w);
if(res == all_light){
first = mid;
hi = mid-1;
}
else{
lo = mid+1;
}
}
assert(first != -1);
int t = -1;
{
auto [u,v] = edges[ord[first]];
if(dis[u] > dis[v]) t = u;
else t = v;
}
answer(s,t);
}
