#include <bits/stdc++.h>
using namespace std;
int press(string p);
string guess_sequence(int N) {
string S = "";
// 找第一個字
if (press("AB")) {
if (press("A")) S = "A";
else S = "B";
} else {
if (press("X")) S = "X";
else S = "Y";
}
vector<char> all = {'A', 'B', 'X', 'Y'};
while ((int)S.size() < N) {
vector<char> cand;
for (char c : all) {
if (c != S[0]) cand.push_back(c);
}
if ((int)S.size() == N - 1) {
// 最後一個
if (press(S + cand[0])) S += cand[0];
else S += cand[1];
break;
}
string query = S + cand[0] + S + cand[1] + S + cand[2];
int res = press(query);
if (res == (int)S.size() + 1) {
S += cand[0];
} else if (res == (int)S.size() + 2) {
S += cand[1];
} else {
S += cand[2];
}
}
return S;
}
