#include <bits/stdc++.h>
using namespace std;
 
int main() {
  int a,b,res;
  cin >> a >>b;
  
  res = -1;
  
  if(a == 0 || b == 0) res = -1;
    
    if(a.size == 1 && b.size == 1){
      res = a*b;
      else{
        res = -1;
      }
    
}