/*
ID: USACO_template
LANG: C++
PROG: https://oj.uz/problem/view/IOI18_combo
*/
#include <iostream> //cin , cout
#include <fstream> //fin, fout
#include <stdio.h> // scanf , pringf
#include <cstdio>
#include <algorithm> // sort , stuff
#include <stack> // stacks
#include <queue> // queues
#include <map>
#include <string>
#include <string.h>
#include <set>
using namespace std;
typedef pair<int, int> pii;
typedef vector<int> vi; /// adjlist without weight
typedef vector<pii> vii; /// adjlist with weight
typedef vector<pair<int,pii>> vpip; /// edge with weight
typedef long long ll;
#define mp make_pair
#define ff first
#define ss second
#define pb push_back
#define sz(x) (int)(x).size()
const int MOD = 1e9+7; // 998244353;
const int MX = 2e5+5; //
const ll INF = 1e18; //
#define MAXV 300007
#define MAXE 100007
bool debug= false;
#include "combo.h"
string guess_sequence(int N) {
string s = "";
vector<string> b = {"A", "B", "X", "Y"};
// find the starting char first
if(press(b[0]+b[1])>0) { // AB or A
if(press(b[0])>0) {
// A
} else { //B
swap(b[0], b[1]);
}
} else if(press(b[2])>0) { // X
swap(b[0], b[2]);
} else {
swap(b[0], b[3]);
}
s += b[0];
// special case
if(N==1) return s;
// build s one by one. case: ABA = +1, AC*A = +2, or AD*A = +0
for(int len=2;len<=N-1; len++) {
string cmd = s+b[1] + s+b[2]+b[1] + s+b[2]+b[2] + s+b[2]+b[3];
int p = press(cmd);
if(p == sz(s)+1) s += b[1];
else if(p == sz(s)+2) s += b[2];
else s += b[3];
}
// last char
for(int i=1; i<4; i++)
if(press(s+b[i])==N) {
s += b[i]; break;
}
return s;
}
