#ifdef NYAOWO
#include "grader.cpp"
#endif
#include "highway.h"
#include <bits/stdc++.h>
#define For(i, a, b) for(int i = a; i <= b; i++)
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define sz(x) ((int)x.size())
#define eb emplace_back
using namespace std;
using LL = long long;
using pii = pair<int, int>;
const int MAXN = 90010;
vector<int> adj[MAXN];
int d[MAXN];
int eid[MAXN];
void dfs(int n, int p, int dep) {
d[n] = dep;
for(auto &i:adj[n]) if(i != p) {
dfs(i, n, dep + 1);
}
}
LL query(const vector<int> &v, int M) {
vector<int> w(M, 0);
for(auto &i:v) w[eid[i]] = 1;
return ask(w);
}
// lowest endpoint > dep ?
bool check(int dep, int N, int M, LL dist) {
vector<int> w(M, 0);
For(i, 0, N) if(d[i] >= dep) {
w[eid[i]] = 1;
}
return ask(w) > dist;
}
int solve(int N, int M, vector<int> &cand, LL dist) {
int m = sz(cand);
if(m == 1) return cand[0];
int mi = m / 2;
vector<int> v1(cand.begin(), cand.begin() + mi);
vector<int> v2(cand.begin() + mi, cand.end());
if(query(v1, M) > dist) return solve(N, M, v1, dist);
return solve(N, M, v2, dist);
}
void find_pair(int N, std::vector<int> U, std::vector<int> V, int A, int B) {
cerr << A << " " << B << "\n";
int M = U.size();
// assert(M == N - 1);
LL dist = ask(vector<int>(M, 0));
assert(dist % A == 0);
For(i, 0, M - 1) {
adj[U[i]].eb(V[i]);
adj[V[i]].eb(U[i]);
}
dfs(0, 0, 0);
For(i, 0, M - 1) {
if(d[U[i]] < d[V[i]]) eid[V[i]] = i;
else eid[U[i]] = i;
}
int hi = N + 1, lo = 0;
while(hi - lo > 1) {
int mi = (hi + lo) / 2;
if(check(mi, N, M, dist)) lo = mi;
else hi = mi;
}
vector<int> cand;
For(i, 0, N - 1) if(d[i] == lo) cand.eb(i);
int rt = solve(N, M, cand, dist);
answer(0, rt);
// dfs(rt, rt, 0);
// For(i, 0, M - 1) {
// if(d[U[i]] < d[V[i]]) eid[V[i]] = i;
// else eid[U[i]] = i;
// }
// cand.clear();
// For(i, 0, N - 1) if(d[i] == dist / A) cand.eb(i);
// answer(rt, solve(N, M, cand, dist));
// for (int j = 0; j < 50; ++j) {
// std::vector<int> w(M);
// for (int i = 0; i < M; ++i) {
// w[i] = 0;
// }
// long long toll = ask(w);
// }
// answer(0, N - 1);
}
