#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <cassert>
using namespace std;
int press(string p);
string guess_sequence(int N)
{
string str;
str.resize(4 * N);
char head;
for(char symbol : {'A', 'B', 'X', 'Y'})
{
std::fill(str.begin(), str.end(), symbol);
if(press(str) == 1)
{
head = symbol;
break;
}
}
assert(head != 0);
string res;
res.push_back(head);
for(int i = 1 ; i < N ; ++i)
{
str.clear();
for(char symbol : {'A', 'B', 'X', 'Y'})
{
str = res;
str.push_back(symbol);
for(int j = i + 1 ; j < 4 * N ; ++j)
{
res[j] = head;
}
if(press(str) == i + 1)
{
res.push_back(symbol);
break;
}
}
}
return res;
}
