import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int s = sc.nextInt();
		sc.close();

		List<String> list = new ArrayList<>();
		int end = power(3, n);
		for (int x = 0; x < end; x++) {
			int x2 = x;
			StringBuilder sb = new StringBuilder();
			for (int i = 0; i < n; i++) {
				sb.append(x2 % 3);
				x2 /= 3;
			}
			sb.reverse();

			StringBuilder sb2 = new StringBuilder();
			for (int i = 0; i < n; i++) {
				sb2.append((char) ('A' + (sb.charAt(i) - '0')));
			}
			String str = sb2.toString();
			if (str.contains("A") && str.contains("B") && str.contains("C")) {
				list.add(str);
			}
		}
		if (list.size() < s) {
			System.out.println(-1);
		} else {
			System.out.println(list.get(s - 1));
		}
	}

	static int power(int x, int n) {
		if (n == 0) {
			return 1;
		}
		int val = power(x, n / 2);
		val = val * val;
		if (n % 2 == 1) {
			val = val * x;
		}
		return val;
	}
}