#include<bits/stdc++.h>
using namespace std;
using ll=long long;

vector<string> S;
ll N;

void dfs(ll N,string R){
	if(R.size()==N){
		int e=0;
		for(int i=0;i<N;i++)e|=(1<<(R[i]-'A'));
		if(e==7)S.push_back(R);
		return;
	}
	for(int i=0;i<3;i++){
		R.push_back('A'+i);
		dfs(N,R);
		R.pop_back();
	}
	return;
}
 
void solve(){
	ll N,SS;
	cin>>N>>SS;
	dfs(N,"");
	if(S.size()<SS)cout<<-1<<endl;
	else cout<<S[SS-1]<<endl;

}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
	
	ll T=1;
	// cin>>T;
	while(T--)
	solve();

}