#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define fst first
#define snd second
#define pb push_back
#define forn(i,a,b) for(int i = a; i < b; i++)
#define ALL(x) x.begin(),x.end()
#define SZ(x) (int)x.size()
#define mset(a,v) memset((a),(v),sizeof(a))
#define FIN ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define dbg(v) cout<<"Line("<<__LINE__<<"): "<<#v<<" = "<<v<<'\n';
#define pi pair<int,int>
#define pll pair<ll,ll>
typedef long long ll;
using namespace std;
using namespace __gnu_pbds;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> indexed_set;
typedef tree<int,null_type,less_equal<int>,rb_tree_tag,tree_order_statistics_node_update> indexed_multiset;
/*
#include "combo.h"
const int MAXC = 4;
char chars[MAXC];
std::string guess_sequence(int N) {
chars[0]='A';
chars[1]='B';
chars[2]='X';
chars[3]='Y';
string aux;
char fChar;
forn(i,0,MAXC){
aux=""; aux+=chars[i];
if(press(aux)){
fChar=chars[i];
break;
}
}
string res = ""; res+=fChar;
forn(i,1,N){
forn(j,0,MAXC) if(chars[j]!=fChar){
if(press(res+chars[j])==i+1){
res+=chars[j];
break;
}
}
}
return res;
}
*/
#include "combo.h"
const int MAXC = 4;
char chars[MAXC];
std::string guess_sequence(int N) {
chars[0]='A';
chars[1]='B';
chars[2]='X';
chars[3]='Y';
string aux;
string res = "";
forn(i,0,N){
aux = res; aux+=chars[0]; aux+=res; aux+=chars[1];
//cout<<aux<<'\n';
if(press(aux)>=i+1){
aux = res; aux+=chars[0];
//cout<<aux<<'\n';
if(press(aux)>=i+1){
res+=chars[0];
}else{
res+=chars[1];
}
}else{
aux = res; aux+=chars[2];
//cout<<aux<<'\n';
if(press(aux)>=i+1){
res+=chars[2];
}else{
res+=chars[3];
}
}
}
cout<<res<<'\n';
return res;
}
