#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define nodes 400005
#define int long long int
void fast(){
	ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
}
main()
{
    int a,b;
    cin>>a>>b;
    if(b>=10)cout<<"-1"<<endl;
    else cout<<(a*b)<<endl;
 
}
