#include<bits/stdc++.h>
#define maxn 10005
#define oo 1000000007
#define ff first
#define ss second
#define sci(x) scanf("%d", &x)
#define scii(x, y) scanf("%d %d", &x, &y)
#define fto(i, a, b) for(int i = a; i <= b; ++i)
#define fdto(i, a, b) for(int i = a; i >= b; --i)
#define pri(x) printf("%d ", x);
#define pril(x) printf("%d\n", x);
#define sz(a) (int)a.size()
#define ii pair<int, int>
#define vi vector<int>
#define vii vector<ii>
#define pb push_back
#define ll long long
#define db double
#define mp make_pair
#define fast cin.sync_with_stdio(0); cin.tie(0)
using namespace std;
int press(string p);
//int press(string p){
// cout << p << endl;
// int x;
// cin >> x;
// return x;
//}
string guess_sequence(int n) {
string p = "";
vector<char> e;
e.pb('A');
e.pb('B');
e.pb('X');
e.pb('Y');
int i = 0;
char check;
while(1){
string s = "";
s += e[i];
if (press(s) == 1){
p += e[i];
check = e[i];
break;
}
++i;
}
int coins = 1;
while(1){
for (int x = 0; x <= sz(e); ++x){
if (check == e[x]) continue;
if (press(p+e[x]) > coins){
++coins;
p += e[x];
break;
}
}
if (coins == n) return p;
}
return p;
}
//int main(){
// int n;
// cin >> n;
// cout << guess_sequence(n) << endl;
//}
