#include <iostream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <numeric>
#include <cstring>
#include <string>
#include <cmath>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
using namespace std;
#define ll long long
#define ull unsigned long long
#define f first
#define s second
#define PF push_front
#define PB push_back
#define MP make_pair
#define max(a, b) ((a > b)? a : b)
#define min(a, b) ((a < b)? a : b)
#define max3(a, b, c) max(max(a, b), c)
#define min3(a, b, c) min(min(a, b), c)
const int N = 2e3 + 5;
const int M = 1e9 + 7;
const int inf = 0x3f3f3f3f;
const ll int INF = 1e18;
int press(string s);
string guess_sequence(int n){
string str = "";
char c[4] = {'A', 'B', 'X', 'Y'};
for(int i = 1; i <= n; i++){
for(int j = 0; j < 4; j++){
int cur = press(str + c[j]);
if(cur == i) {
str += c[j];
break;
}
}
}
return str;
}
// int main(){
// ios::sync_with_stdio(false);
// cin.tie(NULL);
// // ifstream cin();
// // ofstream cout();
// string ans;
// ans = guess_sequence(4);
// cout << ans << endl;
// }
