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 < 10 && B < 10 && A > 0 && B > 0) {
            System.out.println(A*B);
        } else {
            System.out.println(-1);
        }
        
    }
}