#include <bits/stdc++.h>
using namespace std;
int main() {
  int A, B;
  cin >> A >> B;
  if (0 <= A && A <= 9) {
    if (0 <= B && B <= 9) {
      cout << A * B << endl;
    }
  } else {
    cout << "-1" << endl;
  }
}
