#include <iostream>
#include <string>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <vector>
#include <map>
#include <queue> 
#include <stack>

using namespace std;
typedef long long ll;
#define rep(i, s, e) for (int(i) = (s); (i) <= (e); ++(i))
#define all(x) x.begin(),x.end()


int main()
{
	int a,b;
	cin>>a>>b;
	if(a<10&&b<10)cout<<a*b<<endl;;
	else cout<<-1<<endl;
}
