#include <bits/stdc++.h>
using namespace std;
int main() {
  long long a, b;
  cin >> a >> b;
  if (((a > 0) and (a < 10)) and ((b > 0) and (b < 0))) {
    cout << a * b << endl;
  } else {
    cout << "-1" << endl;
  }
}
