Language: C++

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using MessagePack;
using MessagePack.Resolvers;
namespace Capp
{
    class Program
    {
        public enum En
        {
            a
            ,b
            ,c
            ,d
            ,e
            ,f
        }

        
        static void Main(string[] args)
        {
            var c = new Solve();
            c.S();

        }
    }

    public class Solve
    {
        List<int>[] es = new List<int>[10];
        int n;
        int m;
        int res = 0;
        int t = 0;
        void rec(int x)
        {
            if (t == (1 << n) - 1)
            {
                res++;
                return;
            }
            foreach(var v in es[x])
            {
                if ((t & (1 << v)) > 0)
                    continue;
                t |= (1 << v);

                rec(v);
                t ^= (1 << v);
            }
        }
        public void S()
        {
            var nm = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
            n = nm[0];
            m = nm[0];
            for (int i = 0; i < n; i++)
            {
                es[i] = new List<int>();
            }
            for (int i = 0; i < m; i++)
            {
                var s = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
                var a = s[0] - 1;
                var b = s[1] - 1;
                es[a].Add(b);
                es[b].Add(a);
            }
            t = 1;
            rec(0);
            Console.WriteLine(res);
        }
    }

    public class Test<T> : ITest<T>
    {
        public string S { get; set; }
    }

    public interface ITest<out T>
    {
        string S { get; set; }
    }

    struct c
    {
        public string s { get; set; }
        private dynamic _d;
        public dynamic d { get { return _d; }}
        public void Setd(dynamic d)
        {
            _d = d;
        }
    }
    class AsTest
    {
        internal async Task<int> AsyncMethod(int x)
        {
            var t1 = Task.Run(() =>
            {
                Thread.Sleep(10000);
                return 10 * x;
            });
            var res = await t1;
            Console.WriteLine($"asyncmethod {res}");


            return res;
        }

    }
}


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.Threading;
      |       ^~~~~~
a.cc:5:7: error: expected nested-name-specifier before 'System'
    5 | using System.Threading.Tasks;
      |       ^~~~~~
a.cc:6:7: error: expected nested-name-specifier before 'MessagePack'
    6 | using MessagePack;
      |       ^~~~~~~~~~~
a.cc:7:7: error: expected nested-name-specifier before 'MessagePack'
    7 | using MessagePack.Resolvers;
      |       ^~~~~~~~~~~
a.cc:12:15: error: expected ':' before 'enum'
   12 |         public enum En
      |               ^~~~~
      |               :
a.cc:23:26: error: 'string' has not been declared
   23 |         static void Main(string[] args)
      |                          ^~~~~~
a.cc:23:35: error: expected ',' or '...' before 'args'
   23 |         static void Main(string[] args)
      |                                   ^~~~
a.cc:12:16: error: new types may not be defined in a return type
   12 |         public enum En
      |                ^~~~
a.cc:12:16: note: (perhaps a semicolon is missing after the definition of 'Capp::Program::En')
a.cc:12:16: error: two or more data types in declaration of 'Main'
a.cc:29:6: error: expected ';' after class definition
   29 |     }
      |      ^
      |      ;
a.cc:31:5: error: expected unqualified-id before 'public'
   31 |     public class Solve
      |     ^~~~~~
a.cc:78:5: error: expected unqualified-id before 'public'
   78 |     public class Test<T> : ITest<T>
      |     ^~~~~~
a.cc:83:5: error: expected unqualified-id before 'public'
   83 |     public interface ITest<out T>
      |     ^~~~~~
a.cc:90:15: error: expected ':' before 'string'
   90 |         public string s { get; set; }
      |               ^~~~~~~
      |               :
a.cc:90:16: error: 'string' does not name a type
   90 |         public string s { get; set; }
      |                ^~~~~~
a.cc:91:16: error: expected ':' before 'dynamic'
   91 |         private dynamic _d;
      |                ^~~~~~~~
      |                :
a.cc:91:17: error: 'dynamic' does not name a type
   91 |         private dynamic _d;
      |                 ^~~~~~~
a.cc:92:15: error: expected ':' before 'dynamic'
   92 |         public dynamic d { get { return _d; }}
      |               ^~~~~~~~
      |               :
a.cc:92:16: error: 'dynamic' does not name a type
   92 |         public dynamic d { get { return _d; }}
      |                ^~~~~~~
a.cc:93:15: error: expected ':' before 'void'
   93 |         public void Setd(dynamic d)
      |               ^~~~~
      |               :
a.cc:93:26: error: 'dynamic' has not been declared
   93 |         public void Setd(dynamic d)
      |                          ^~~~~~~
a.cc:97:6: error: expected ';' after struct definition
   97 |     }
      |      ^
      |      ;
a.cc: In member function 'void Capp::c::Setd(int)':
a.cc:95:13: error: '_d' was not declared in this scope; did you mean 'd'?
   95 |             _d = d;
      |             ^~
      |             d
a.cc: At global scope:
a.cc:100:9: error: 'internal' does not name a type
  100 |         internal async Task<int> AsyncMethod(int x)
      |         ^~~~~~~~
a.cc:114:6: error: expected ';' after class definition
  114 |     }
      |      ^
      |      ;