#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/tree_policy.hpp>
#include <functional> // for less
#include <iostream>
using namespace __gnu_pbds;
using namespace std;

#define pf(n) cout << n << endl
#define ps() cout <<" ";
#define sf(n) cin >> n
#define in(i,n) for (int i = 0; i < n; i++)
#define vi vector<int>
#define vp vector<pair<int, int>>
#define graph vector< vector<int> >
#define vs vector<string>
/**  '' "\n" ^ - **/

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    int a,b;
    if(a<10&&b<10)cout<<a*b;
    else cout<<-1;
}
