import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    if (a >= 1 && a <= 9 && b >= 1 && b <= 9)
      System.out.println(a * b);
    else
      System.out.println(-1);
  }
}