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