#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000005
#define Inf64 4000000000000000001LL
vector<string> s;
void dfs(int n,string t){
	if(n==0){
		int tt = 0;
		rep(i,t.size()){
			tt |= 1<<(t[i] - 'A');
		}
		if(tt==7)s.push_back(t);
		
	}
	else{
		dfs(n-1,t + 'A');
		dfs(n-1,t + 'B');
		dfs(n-1,t + 'C');
	}
}
int main(){
	
	int n;
	cin>>n;
	dfs(n,"");
	int ii;
	cin>>ii;
	ii--;
	if(ii>=s.size()){
		cout<<-1<<endl;
		return 0;
	}
	cout<<s[ii]<<endl;
	return 0;
}