Language: C++

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder
{
    class Program
    {
        static long ReadLong()
        {
            return long.Parse(Console.ReadLine());
        }

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

        static double ReadDouble()
        {
            return double.Parse(Console.ReadLine());
        }

        static double[] ReadDoubles()
        {
            return Console.ReadLine().Split(' ').Select(double.Parse).ToArray();
        }

        static string ReadString()
        {
            return Console.ReadLine();
        }

        static string[] ReadStringSplit()
        {
            return Console.ReadLine().Split(' ');
        }

        static void A()
        {
            var AB = ReadLongs();
            var A = AB[0];
            var B = AB[1];
            Console.WriteLine(Math.Max(A - (2 * B), 0));
        }

        static void B()
        {

        }

        static void C()
        {

        }

        static void D()
        {

        }

        static void Main(string[] args)
        {
            A();
            //B();
            //C();
            //D();
        }
    }
}


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.Collections.Generic;
      |       ^~~~~~
a.cc:3:7: error: expected nested-name-specifier before 'System'
    3 | using System.Linq;
      |       ^~~~~~
a.cc:4:7: error: expected nested-name-specifier before 'System'
    4 | using System.Text;
      |       ^~~~~~
a.cc:5:7: error: expected nested-name-specifier before 'System'
    5 | using System.Threading.Tasks;
      |       ^~~~~~
a.cc:16:20: error: expected unqualified-id before '[' token
   16 |         static long[] ReadLongs()
      |                    ^
a.cc:26:22: error: expected unqualified-id before '[' token
   26 |         static double[] ReadDoubles()
      |                      ^
a.cc:31:16: error: 'string' does not name a type
   31 |         static string ReadString()
      |                ^~~~~~
a.cc:36:16: error: 'string' does not name a type
   36 |         static string[] ReadStringSplit()
      |                ^~~~~~
a.cc:64:26: error: 'string' has not been declared
   64 |         static void Main(string[] args)
      |                          ^~~~~~
a.cc:64:35: error: expected ',' or '...' before 'args'
   64 |         static void Main(string[] args)
      |                                   ^~~~
a.cc:71:6: error: expected ';' after class definition
   71 |     }
      |      ^
      |      ;
a.cc: In static member function 'static long int AtCoder::Program::ReadLong()':
a.cc:13:20: error: expected primary-expression before 'long'
   13 |             return long.Parse(Console.ReadLine());
      |                    ^~~~
a.cc:13:20: error: expected ';' before 'long'
a.cc:13:24: error: expected unqualified-id before '.' token
   13 |             return long.Parse(Console.ReadLine());
      |                        ^
a.cc: In static member function 'static double AtCoder::Program::ReadDouble()':
a.cc:23:20: error: expected primary-expression before 'double'
   23 |             return double.Parse(Console.ReadLine());
      |                    ^~~~~~
a.cc:23:20: error: expected ';' before 'double'
a.cc:23:26: error: expected unqualified-id before '.' token
   23 |             return double.Parse(Console.ReadLine());
      |                          ^
a.cc: In static member function 'static void AtCoder::Program::A()':
a.cc:43:13: error: 'var' was not declared in this scope
   43 |             var AB = ReadLongs();
      |             ^~~
a.cc:44:17: error: expected ';' before 'A'
   44 |             var A = AB[0];
      |                 ^
a.cc:45:17: error: expected ';' before 'B'
   45 |             var B = AB[1];
      |                 ^
a.cc:46:13: error: 'Console' was not declared in this scope
   46 |             Console.WriteLine(Math.Max(A - (2 * B), 0));
      |             ^~~~~~~
a.cc:46:31: error: 'Math' was not declared in this scope
   46 |             Console.WriteLine(Math.Max(A - (2 * B), 0));
      |                               ^~~~
a.cc:46:47: error: invalid operands of types 'int' and 'void()' to binary 'operator*'
   46 |             Console.WriteLine(Math.Max(A - (2 * B), 0));
      |                                             ~~^~~