Language: C++

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

namespace ABC113A
{
    static class MainClass
    {
        public static void Main(string[] args)
        {

            string[] input1 = Console.ReadLine().Split(' ');
            int N = int.Parse(input1[0]);

            if(N == 1){
                Console.WriteLine("Hello World");
                return;
            }


            int A = int.Parse(Console.ReadLine());
            int B = int.Parse(Console.ReadLine());

            Console.WriteLine(A + B);
            return;

        }


        public static int Gcd(int a, int b)
        {
            int tmp;
            // a<bにする
            if (a >= b)
            {
                tmp = a;
                a = b;
                b = tmp;
            }

            if (a == 0)
            {
                return b;
            }

            tmp = a;
            a = b % a;
            b = tmp;
            return Gcd(a, b);

        }


    }

}






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:9:15: error: expected ':' before 'static'
    9 |         public static void Main(string[] args)
      |               ^~~~~~~
      |               :
a.cc:9:33: error: 'string' has not been declared
    9 |         public static void Main(string[] args)
      |                                 ^~~~~~
a.cc:9:42: error: expected ',' or '...' before 'args'
    9 |         public static void Main(string[] args)
      |                                          ^~~~
a.cc:30:15: error: expected ':' before 'static'
   30 |         public static int Gcd(int a, int b)
      |               ^~~~~~~
      |               :
a.cc:54:6: error: expected ';' after class definition
   54 |     }
      |      ^
      |      ;
a.cc: In static member function 'static void ABC113A::MainClass::Main(int*)':
a.cc:12:13: error: 'string' was not declared in this scope
   12 |             string[] input1 = Console.ReadLine().Split(' ');
      |             ^~~~~~
a.cc:12:20: error: expected primary-expression before ']' token
   12 |             string[] input1 = Console.ReadLine().Split(' ');
      |                    ^
a.cc:13:21: error: expected primary-expression before 'int'
   13 |             int N = int.Parse(input1[0]);
      |                     ^~~
a.cc:16:17: error: 'Console' was not declared in this scope
   16 |                 Console.WriteLine("Hello World");
      |                 ^~~~~~~
a.cc:21:21: error: expected primary-expression before 'int'
   21 |             int A = int.Parse(Console.ReadLine());
      |                     ^~~
a.cc:22:21: error: expected primary-expression before 'int'
   22 |             int B = int.Parse(Console.ReadLine());
      |                     ^~~
a.cc:24:13: error: 'Console' was not declared in this scope
   24 |             Console.WriteLine(A + B);
      |             ^~~~~~~
a.cc: At global scope:
a.cc:7:5: error: a storage class can only be specified for objects and functions
    7 |     static class MainClass
      |     ^~~~~~