z#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <string>
#include <numeric>
#include <cmath>

#define rep(i, n) for (int i = 0; i < n; i++)
using namespace std;
typedef long long ll;
using P = pair<ll, ll>;

template<class T> inline bool chmin(T& a,T b) {if (a > b) {a = b; return true;} return false;}
template<class T> inline bool chmax(T& a,T b) {if (a < b) {a = b; return true;} return false;}

const ll MOD = 1000000007;
const int INF = 1<<29;

int main(){
  int A, B;
  if (1 <= A && A <= 9 && 1 <= B && B <= 9) cout << A * B << endl;
  else cout << -1 << endl;
}
