#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define rep(i, n) for (ll i = 0; i < n; i++)
#define FOR(i, a, b) for (ll i = a; i < b; i++)
#define len(v) ll(v.size())

template <class T>
void cout_vec(const vector<T> &vec1){
  rep(i,len(vec1)){
    cout<<vec1[i]<<' ';
  }
  cout<<'\n';
}

typedef pair<ll,ll> P;

const ll mod=1e9+7;

ll gcd(ll a, ll b){
    ll r;
    while((r =a%b)){
        a = b;
        b = r;
    }
    return b;
}


int main(){

  int A,B;
  cin >> A >> B;

  if ( A <10 && B < 10){
    cout << N * X << endl;
  } else {
    cout << -1 << endl;
  }

  return 0;

}