//------------------------------------------------------------------------------MANAS UNIYAL---------------------------------------------------------
//																				NEVER GIVE UP
#include<bits/stdc++.h>
using namespace std;
#define fast ios_base::sync_with_stdio(false);	cin.tie(NULL);	cout.tie(NULL);
#define ll long long
#define pb push_back
#define fi first
#define se second
#define pii pair<ll,ll>
#define INF 0x3f3f3f3f
#define mod 100000007
#define testcases() ll t; cin>>t; while(t--)
#define debug1(x) cout<<#x<<" "<<x<<"\n";
#define debug2(x,y) cout<<#x<<" "<<x<<" "<<#y<<" "<<y<<"\n";
#define debug3(x,y,z) cout<<#x<<" "<<x<<" "<<#y<<" "<<y<<" "<<#z<<" "<<z<<"\n";
#define rep(i,start,end) for(ll i=start;i<end;i++)
 
//----------------------------------------------------------------------------------------------------------------------------------------------------

int main()
{
	fast;
	cin>>a>>b;
	if(a<=9 && b<=9)
		cout<<a*b;
	else 
		cout<<"-1";
	return 0;
}