#include <bits/stdc++.h>
#include "highway.h"
using namespace std;
using ll = long long;
void find_pair(int N, vector<int> U, vector<int> V, int A, int B) {
int M = size(U), x = 0, u, d[2][N];
vector<int> w(M);
ll least = ask(w);
for(int b = 1<<17; b/=2; ) if(x + b < M) {
fill(begin(w), begin(w) + x + b, 1);
bool ok = ask(w) == least;
fill(begin(w), begin(w) + x + b, 0);
if(ok) x |= b;
}
array<int, 2> S = {U[x], V[x]}, ans {};
vector<array<int, 2>> g[N], a;
for(int i = x; i < M; i++) {
g[U[i]].push_back({V[i], i});
g[V[i]].push_back({U[i], i});
}
for(int k : {0, 1}) {
fill(d[k], d[k] + N, N);
queue<int> q;
d[k][S[k]] = 0;
q.push(S[k]);
while(!empty(q)) {
u = q.front(); q.pop();
for(auto &[v, e] : g[u]) if(d[k][v] > d[k][u] + 1)
d[k][v] = d[k][u] + 1, q.push(v);
}
}
for(int k : {0, 1}) {
a.clear();
for(int i = 0; i < N; i++)
if(d[k][i] < d[!k][i]) a.push_back({-d[k][i], i});
sort(begin(a), end(a));
for(int b = 1<<17; b/=2; ) if(ans[k] + b < size(a)) {
fill(begin(w), begin(w) + x, 1);
for(int i = ans[k] + b; --i >= 0; )
for(auto &[v, e] : g[a[i][1]])
w[e] = 1;
bool ok = ask(w) == least;
for(int i = ans[k] + b; --i >= 0; )
for(auto &[v, e] : g[a[i][1]])
w[e] = 0;
fill(begin(w), begin(w) + x, 0);
if(ok) ans[k] |= b;
}
ans[k] = a[ans[k]][1];
}
answer(ans[0], ans[1]);
}
