#include <bits/stdc++.h>
#include "highway.h"
using namespace std;
using ll = long long;
using pii = pair<int, int>;
vector<int> query;
vector<int> s;
vector<int> u, v;
bool diff() {
int m = query.size();
for (int i=0; i<m; i++) {
query[i] = (s[u[i]] == s[v[i]]);
}
ll w = ask(query);
return (w%2==1);
}
void find_pair(int N, vector<int> U, vector<int> V, int A, int B) {
int m = U.size();
u = U, v = V;
query.assign(m, 0);
s.assign(N, 0);
vector<int> grp;
int xr=0;
for (int b=0; b<17; b++) {
for (int i=0; i<N; i++) {
s[i] = !!(i&(1<<b));
}
if (diff()) {
xr |= (1<<b);
grp = s;
}
}
int l = 0, r = N-1;
int ans = 0;
while (l <= r) {
int mid = (l+r)/2;
for (int i=0; i<N; i++) {
s[i] = (grp[i] && l <= i && i <= mid);
}
if (diff()) {
r = mid-1;
}
else {
l = mid+1;
ans = mid+1;
}
}
answer(ans, ans^xr);
}
