#include <bits/stdc++.h>
#ifndef LOCAL
#include "combo.h"
#endif
using namespace std;
#define REP(i, n) for (int i = 0; i < (n); i++)
#ifdef LOCAL
int press(string s);
#endif
const int M = 4;
const char ABC[] = "ABXY";
string guess_sequence(int N) {
string s;
int len[M];
REP(i, N) {
bool found = false;
REP(j, M-1) {
len[j] = press(s + ABC[j]);
if (len[j] == i+1) {
s += ABC[j];
found = true;
break;
}
}
if (!found) {
s += ABC[M-1];
}
}
return s;
}
#ifdef LOCAL
string SECRET = "ABXYYB";
int press(string p) {
const int m = p.length();
const int n = SECRET.length();
int lpref = 0;
REP(i, m) {
int j = 0;
while (j < n && i+j < m && SECRET[j] == p[i+j]) {j++;}
lpref = max(lpref, j);
}
return lpref;
}
int main() {
cout << guess_sequence(SECRET.length()) << '\n';
}
#endif
