#include <bits/stdc++.h>
#define int long long
#define rep(i,n) for(int i=0;i<n;++i)
#define rep1(i,n) for(int i=1;i<=n;++i)
#define all(a) a.begin(),a.end()
#define P pair<long long,long long>
#define double long double
using namespace std;
//桁
int kt(int a){
  double b=a;
  b=log10(b);
  int c=b;
  return c+1;
 }
int lcm(int a,int b){
  int d=a,e=b,f;
  if(a<b)
    swap(a,b);
  int c,m=1;
  while(m){
    c=a%b;
    if(c==0){
       f=b;
      m--;
    }
    else{
      a=b;
      b=c;
 }
  }
  return d*e/f;
    }
  int gcm(int a,int b){
      int d=a,e=b,f;
  if(a<b)
    swap(a,b);
  int c,m=1;
  while(m){
    c=a%b;
    if(c==0){
       f=b;
      m--;
    }
    else{
      a=b;
      b=c;
 }
  }
  return f;
  }
signed main(){
  int a,b;
  cin>>a>>b;
  if(1<=a&&a<=9&&1<=b&&&b<=9)
    cout<<a*b;
  else
    cout<<-1;
}