#include<bits/stdc++.h>
using namespace std;
#define ll int64_t
#define f first
#define sec second
#define pb push_back
#define pf push_front
#define po pop_back
#define fast ios_base::sync_with_stdio(false)
#define vi vector<ll>
#define vii vector< pair<ll,ll> >
#define pi pair<ll,ll>
#define map map<ll,ll>
#define set set<ll>
#define tostr to_string
#define toint stoi
#define gcd __gcd


int main()
{
  lla,b;cin>>a>>b;
  if((a<=9)&&(b<=9))
    cout<<a*b<<endl;
  else
    cout<<-1<<endl;
}
