#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, b;
  cout << "Pleas Enter Two Numbers : ";
  cin >> a >> b;
  1 <= a <= 20;
  1 <= b <= 20;
  if (a >= 10 or b >= 10) {
    cout << "-1";
  } else if ((a <= 9 && a > 0) && (b <= 9 && b > 0)) {
    cout << a * b;
  } else {
    cout << "-1";
  }
  return 0;
}
