#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, b;
  cin >> a >> b;
  if (a < 1 || a > 9 || b < 1 || b >> 9) {
    cout << -1 << endl;
  } else {
    cout << a * b << endl;
  }
  return 0;
}
