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

#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define FORR2(x,y,arr) for(auto& [x,y]:arr)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
template<class T> bool chmax(T &a, const T &b) { if(a<b){a=b;return 1;}return 0;}
template<class T> bool chmin(T &a, const T &b) { if(a>b){a=b;return 1;}return 0;}
//-------------------------------------------------------

int N,M;
vector<string> V;

void dfs(string& S,int mask) {
	if(S.size()==N) {
		if(mask==7) {
			V.push_back(S);
		}
		return;
	}
	int i;
	FOR(i,3) {
		S+='A'+i;
		dfs(S,mask|(1<<i));
		S.pop_back();
	}
}

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N>>M;
	string S;
	dfs(S,0);
	
	if(V.size()>=M) {
		cout<<V[M-1]<<endl;
	}
	else {
		cout<<-1<<endl;
	}
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}