#ifndef davele
#include "combo.h"
#endif // davele
#include <bits/stdc++.h>
#define pq priority_queue
#define ll long long
#define pii pair<int, int>
#define fi first
#define se second
#define pb push_back
#define MASK(i) (1ll<<(i))
#define next __next
#define pos __pos
using namespace std;
const double PI = acos(-1);
/*const int mod = ;
void sub (int&a, const int&b){
a-=b;
if (a<0) a+=mod;
}
void mul (int&a, const int&b){
a = (1ll*a*b)%mod;
}
void add (int&a, const int&b){
a+=b;
if (a>=mod) a-=mod;
}*/
bool minimize (ll&a, const ll&b){
if (a<=b) return false;
a=b;
return true;
}
bool maximize (ll&a, const ll&b){
if (a>=b) return false;
a=b;
return true;
}
////////////////////////////////////////////////////////////////////////////////////////////
string tt[4];
#ifndef davele
string guess_sequence(int n) {
tt[0] = "A"; tt[1] = "B"; tt[2] = "X"; tt[3] = "Y";
int startletter;
if (press(tt[0]+tt[1])>0){
if (press(tt[0])>0) startletter = 0;
else startletter = 1;
}
else{
if (press(tt[2])>0) startletter = 2;
else startletter = 3;
}
string ret = tt[startletter];
if (n==1) return ret;
string cur[3];
//
int len = 0;
for (int i=0; i<4; i++) if (i!=startletter) cur[len++] = tt[i];
for (int i=1; i+1<n; i++){
int get = press(ret+cur[0]+ret+cur[1]+cur[0]+ret+cur[1]+cur[1]+ret+cur[1]+cur[2]);
if (get==i){
ret+=cur[2];
}
else if (get==i+1) ret+=cur[0];
else ret+=cur[1];
}
string ans;
if (press(ret+cur[0])==n){
ans = ret + cur[0];
}
else if (press(ret+cur[1])==n) ans = ret + cur[1];
else ans = ret + cur[2];
return ans;
}
#endif // davele
#ifdef davele
string s;
int N, tot = 0;
int press(const string&p){
tot++;
// cerr<<N<<" "<<p.size()<<"\n";
if (p.size()>N*4){
cerr<<"FALSSEESS"<<"\n";
}
int coins = 0;
int len = p.length();
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 = std::max(coins, j);
}
return coins;
}
string guess_sequence(int n) {
tt[0] = "A"; tt[1] = "B"; tt[2] = "X"; tt[3] = "Y";
int startletter;
if (press(tt[0]+tt[1])){
if (press(tt[0])) startletter = 0;
else startletter = 1;
}
else{
if (press(tt[2])) startletter = 2;
else startletter = 3;
}
string ret = tt[startletter];
string cur[3];
int len = 0;
for (int i=0; i<4; i++) if (i!=startletter) cur[len++] = tt[i];
for (int i=1; i+1<n; i++){
int get = press(ret+cur[0]+ret+cur[1]+cur[0]+ret+cur[1]+cur[1]+ret+cur[1]+cur[2]);
if (get==i){
ret+=cur[2];
}
else if (get==i+1) ret+=cur[0];
else ret+=cur[1];
}
if (press(ret+cur[0])==n) return (ret+cur[0]);
else if (press(ret+cur[1])==n) return (ret+cur[1]);
return (ret+cur[2]);
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
freopen("combo.inp", "r", stdin);
freopen("combo.out", "w", stdout);
cin>>s;
N = s.size();
// cerr<<N<<"\n";
cout<<guess_sequence(N);
// cerr<<"\n"<<tot;
}
#endif // davele
