
import java.util.*;

public class Main {


	public static void main (String [] args) {
		
		
		int a,b;
		
		Scanner sc = new Scanner(System.in);
		
		do {
			a = sc.nextInt();			
		}while(!((a >= 1)&&(a <= 20)));
		
		do {
			b = sc.nextInt();			
		}while(!((b >= 1)&&(b <= 20)));
		
		
		if((a>=1 && a<=9) && (b>=1 && b<=9) ) {
			
			System.out.println(a*b);
			
		}else {
			System.out.println(-1);
		}
		
		
	}
}
		
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz