import java.util.Scanner;

public static void main(String[] args) {
	Scanner scanner = new Scanner(System.in);
  	int a = scanner.nextInt();
  	int b = scanner.nextInt();
  	scanner.close();
  	if (a < 1 || a > 9 || b < 1 || b > 9) {
      	System.out.print("-1");
    	return;
    }
  	System.out.printf("%d", a * b);
}