#pragma GCC optimize("Ofast")
#pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#define f0r(i, n) for (auto i = 0; i < (n); ++i)
#define fnr(i, n, k) for (auto i = (n); i < (k); ++i)
#define all(v) (v).begin(), (v).end()
#define pb push_back
#define F first
#define S second
#define ctn(x) cout << x << '\n'
#define forl(a, l) for (auto a : l)
#define ctl(l) for (auto &a : (l)) cout << a << ' '; cout << endl;
#define lb(v, x) (lower_bound(all(v), x) - begin(v))
#define ub(v, x) (upper_bound(all(v), x) - begin(v))
#define pq priority_queue
template <class T>
using V = vector<T>;
using ll = long long;
using vi = V<int>;
using vl = V<ll>;
using pi = pair<int, int>;
using ti = tuple<int, int, int>;
using Adj = V<vi>;
using vvi = V<vi>;
#include "combo.h"
V<char> chr{'A', 'B', 'X', 'Y'};
string guess_sequence(int N) {
string S = "";
f0r(i, 3) if (press(S+chr[i])) {
swap(chr[i], chr[3]);
break;
}
S += chr.back();
while (S.size() < N-2) {
string T = S+chr[0]+(S+chr[1]+chr[0])+(S+chr[1]+chr[1])+(S+chr[1]+chr[2]);
if (T.size() > 4*N) return "";
int l = press(T);
if (l == S.size()) S += chr[2];
else if (l == S.size()+1) S += chr[0];
else S += chr[1];
}
if (N >= 2) {
if (press(S+chr[0]) == S.size()+1) S += chr[0];
else if (press(S+chr[1]) == S.size()+1) S += chr[1];
else S += chr[2];
}
if (N >= 3) {
if (press(S+chr[0]) == S.size()+1) S += chr[0];
else if (press(S+chr[1]) == S.size()+1) S += chr[1];
else S += chr[2];
}
return S;
}
