import java.util.*;

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 <= 9 && B <= 9) {
      System.out.println(A * B);
    } else {
      System.out.println("-1");
    }
  }
}