import java.util.*;
 
public class Main{
  public static void main (String args[]){
    Scanner sc = new Scanner(System.in);
    int numA = sc.nextInt();
    int numB = sc.nextInt();
    int ans = 0;
    
    if (numA <= 9 && numB <= 9){
      ans = numA*numB;
    } else {
      ans = -1;
    }
    System.out.println(ans);
  }
}
/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