#include <bits/stdc++.h>
using namespace std;
int main(){
int a,b;
cin>>a>>b;
int prod=0;
if( a>=1 && a<=9){
    if(b>=1 && b<=9){
            prod = a*b;
    		}


	}
if(prod)cout<<prod<<endl;
else cout<<-1<<endl;	

}