#include<stdio.h>
int main()
{
  int A,B,c;
  A<=20||A>=1||B<=20||B>=1;
  printf(" ");
  scanf("%d%d",&A，&B);
  if(A>=1||A<=10||B<=10||B>=1)
    c=A*B;
  else 
    c=-1;
  printf("%d\n",c);
  return 0;
}
  