#include "highway.h"
#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> pii;
typedef long long ll;
const int maxn = 1e5 + 100;
int n, m;
vector<pii> g[maxn];
vector<int> s[2];
int t[maxn];
int f[maxn];
int d[maxn];
ll dist;
int calc(vector<int> s){
int v = -1;
for(int l = 0, r = s.size()-1; l <= r;){
int mid = (l + r) >> 1;
vector<int> q(m, 0);
for(int i = 0; i <= mid; i++){
q[f[s[i]]] = 1;
} if(ask(q) == dist) l = mid + 1;
else r = mid - 1, v = s[mid];
} return v;
}
void find_pair(int N, std::vector<int> U, std::vector<int> V, int A, int B) {
n = N; m = U.size();
dist = ask(vector<int>(m, 0));
for(int i = 0; i < m; i++){
int a = U[i], b = V[i];
g[a].push_back({b, i});
g[b].push_back({a, i});
}
int i;
for(int l = 0, r = m-1; l <= r;){
int mid = (l + r) >> 1;
vector<int> q(m, 0);
for(int j = 0; j <= mid; j++){
q[j] = 1;
}
if(ask(q) == dist) l = mid + 1;
else r = mid - 1, i = mid;
}
fill(t, t + n, -1);
t[V[i]] = 1;
t[U[i]] = 0;
queue<int> q;
q.push(V[i]);
q.push(U[i]);
while(q.size()){
int v = q.front();
q.pop();
for(auto [to, i]: g[v]){
if(t[to] == -1){
d[to] = d[v] + 1;
t[to] = t[v];
s[t[v]].push_back(to);
f[to] = i;
q.push(to);
}
}
} vector<int> ans = {U[i], V[i]};
for(int c = 0; c < 2; c++){
reverse(s[c].begin(), s[c].end());
vector<int> q(m, 1);
for(int l = 0, r = s[c].size()-1; l <= r;){
int mid = (l + r) >> 1;
vector<int> q(m, 1);
for(int x: s[0]) q[f[x]] = 0;
for(int x: s[1]) q[f[x]] = 0;
q[i] = 0;
for(int i = 0; i <= mid; i++){
q[f[s[c][i]]] = 1;
} if(ask(q) == dist) l = mid + 1;
else r = mid - 1, ans[c] = s[c][mid];
}
} answer(ans[0], ans[1]);
// cout << ans[0] << ' ' << ans[1] << ' ' << 1ll * A * (d[ans[0]] + d[ans[1]] + 1) << endl;
// cout << dist << ' ' << 1ll * A * (d[S] + d[T] + 1) << endl;
// cout << t[S] << ' ' << t[T] << endl;
// cout << a << ' ' << b << endl;
}
