import java.util.Map;
import java.util.Scanner;
import java.util.TreeMap;

public class Main {
	public static void main(String[] args) throws Exception {
		long t1 = System.currentTimeMillis();
		long end = t1 + 4700;
		Scanner sc = new Scanner(System.in);
		long l = sc.nextLong();
		long r = sc.nextLong();
		sc.close();

		for (long i = l; i <= r; i++) {
			if (i % 2 == 0) {
				continue;
			}
			if (System.currentTimeMillis() > end) {
				break;
			}
			Map<Long, Integer> map = bunkai(i);
			if (map.size() == 3) {
				Integer[] arr = map.values().toArray(new Integer[0]);
				if (arr[0] == 2 && arr[1] == 1 && arr[2] == 1) {
					System.out.println(i);
					return;
				}
			}
		}
		System.out.println(-1);
	}

	static Map<Long, Integer> bunkai(long n) {
		Map<Long, Integer> soinsu = new TreeMap<>();
		int end = (int) Math.sqrt(n);
		long d = 2;
		while (n > 1) {
			if (n % d == 0) {
				n /= d;
				soinsu.put(d, soinsu.getOrDefault(d, 0) + 1);
				end = (int) Math.sqrt(n);
			} else {
				if (d > end) {
					d = n - 1;
				}
				d++;
			}
		}
		return soinsu;
	}
}