function Main(input)
{
  let result = -1;
  let numA = input[0]
  let numB = input[1]

  if (numA < 9 && numB < 9)
  { 
    result = numA * numB;
  }
  
	//出力
  console.log(result);
}

Main(require("fs").readFileSync("/dev/stdin", "utf8"));