#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i< (n); ++i)
#define repi(i, a, b) for (int i = (a); i < (b); ++i)
#define all(x) (x).begin(), (x).end()
#define fore(i, a) for(auto &i:a)
using ll = long long;

int main() {
	int n; cin >> n;
	int s; cin >> s;
  vector<string> st;
	int n3 = 1;
	rep(i, n){
		n3*=3;
	}
	rep(i, n3){
		int b = i;
		string res(n, ' ');
		bool eA = false,eB=false,eC=false;
		rep(i, n){
			if(b%3 == 0){
				res[n-1-i] = 'A';
				eA = true;
			}
			else if(b%3 == 1){
				res[n-1-i] = 'B';
				eB = true;
			}
			else{
				res[n-1-i] = 'C';
				eC = true;
			}
			b/=3;
		}
		if(eA&&eB&&eC){
			st.push_back(res);
		}
	}
	sort(all(st));
	if(st.size() < s)cout << -1 << endl;
	else cout << st[s-1] << endl;
}