#include <bits/stdc++.h>
#include "combo.h"
using namespace std;
/*
int N;
string S;
int press(string p){
int len = p.length();
int coins = 0;
for (int i = 0, j = 0; i < len; ++i) {
if (j < N && S[j] == p[i]) {
++j;
} else if (S[0] == p[i]) {
j = 1;
} else {
j = 0;
}
coins = max(coins, j);
}
return coins;
}
*/
string guess_sequence(int N){
string ans = "";
bool back = true;
while(ans.size() < N){
if(back){
string ck1 = ans + 'A';
string ck2 = ans + 'B';
string ck3 = ans + 'X';
string ck4 = ans + 'Y';
if(press(ck1) == ck1.size()) ans += 'A';
else if(press(ck2) == ck2.size()) ans += 'B';
else if(press(ck3) == ck3.size()) ans += 'X';
else if(press(ck4) == ck4.size()) ans += 'Y';
else back = false;
}
if(!back){
string ck1 = 'A' + ans;
string ck2 = 'B' + ans;
string ck3 = 'X' + ans;
string ck4 = 'Y' + ans;
if(press(ck1) == ck1.size()) ans = ck1;
else if(press(ck2) == ck2.size()) ans = ck2;
else if(press(ck3) == ck3.size()) ans = ck3;
else if(press(ck4) == ck4.size()) ans = ck4;
}
}
return ans;
}
/*int main(){
cin.tie(nullptr)->sync_with_stdio(false);
cin >> N >> S;
cout << guess_sequence(N);
}*/
