import java.util.*;

class Main{
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
int A = sc.nextInt();
int B = sc.nextInt();

if(1<=A && A<=9 && 1<=B && B<=9){

System.out.println(A*B);

} else {
System.out.println(-1);
}
} 
}