Language: C++

using System;
using System.Linq;
using System.Collections.Generic;
using System.IO;


class Program
{
    public static long Read()
    {
        return long.Parse(Console.ReadLine());
    }

    public static long[] Reads()
    {
        return Console.ReadLine().Split().Select(long.Parse).ToArray();
    }

    public static void Main()
    {
        var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
        Console.SetOut(sw);

        var input = Reads();
        var a = input[0];
        var b = input[1];
        if (a > 9 || b > 9)
            Console.WriteLine("-1");
        else
            Console.WriteLine(a * b);



        Console.Out.Flush();
    }
}


Compiler output:
a.cc:1:7: error: expected nested-name-specifier before 'System'
    1 | using System;
      |       ^~~~~~
a.cc:2:7: error: expected nested-name-specifier before 'System'
    2 | using System.Linq;
      |       ^~~~~~
a.cc:3:7: error: expected nested-name-specifier before 'System'
    3 | using System.Collections.Generic;
      |       ^~~~~~
a.cc:4:7: error: expected nested-name-specifier before 'System'
    4 | using System.IO;
      |       ^~~~~~
a.cc:9:11: error: expected ':' before 'static'
    9 |     public static long Read()
      |           ^~~~~~~
      |           :
a.cc:14:11: error: expected ':' before 'static'
   14 |     public static long[] Reads()
      |           ^~~~~~~
      |           :
a.cc:14:23: error: expected unqualified-id before '[' token
   14 |     public static long[] Reads()
      |                       ^
a.cc:19:11: error: expected ':' before 'static'
   19 |     public static void Main()
      |           ^~~~~~~
      |           :
a.cc:36:2: error: expected ';' after class definition
   36 | }
      |  ^
      |  ;
a.cc: In static member function 'static long int Program::Read()':
a.cc:11:16: error: expected primary-expression before 'long'
   11 |         return long.Parse(Console.ReadLine());
      |                ^~~~
a.cc:11:16: error: expected ';' before 'long'
a.cc:11:20: error: expected unqualified-id before '.' token
   11 |         return long.Parse(Console.ReadLine());
      |                    ^
a.cc: In static member function 'static void Program::Main()':
a.cc:21:9: error: 'var' was not declared in this scope
   21 |         var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
      |         ^~~
a.cc:22:9: error: 'Console' was not declared in this scope
   22 |         Console.SetOut(sw);
      |         ^~~~~~~
a.cc:22:24: error: 'sw' was not declared in this scope
   22 |         Console.SetOut(sw);
      |                        ^~
a.cc:24:13: error: expected ';' before 'input'
   24 |         var input = Reads();
      |             ^~~~~
a.cc:25:13: error: expected ';' before 'a'
   25 |         var a = input[0];
      |             ^
a.cc:26:13: error: expected ';' before 'b'
   26 |         var b = input[1];
      |             ^
a.cc:27:13: error: 'a' was not declared in this scope
   27 |         if (a > 9 || b > 9)
      |             ^
a.cc:27:22: error: 'b' was not declared in this scope
   27 |         if (a > 9 || b > 9)
      |                      ^