Language: C

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using static System.Console;
using static System.Math;

namespace Atcoder
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                Solve.Answer();
            }
            catch (Exception ex)
            {
                WriteLine(ex.ToString());
            }
        }
    }

    static class Solve
    {
        public static void Answer()
        {
            var N = IO_ShortCut.ReadInt;
            long ans = 0;
            for (int i = 1; i <= N; i++)
            {
                if (i % 3 == 0 || i % 5 == 0)
                    continue;

                ans += i;
            }
            WriteLine(ans);
        }
    }

    static class IO_ShortCut
    {
        #region Input
        public static string ReadString => ReadLine();
        public static int ReadInt => int.Parse(ReadLine());
        public static long ReadLong => long.Parse(ReadLine());
        public static double ReadDouble => double.Parse(ReadLine());

        public static List<string> ReadSplitString => ReadLine().Split().ToList();
        public static List<int> ReadSplitInt => ReadLine().Split().Select(s => int.Parse(s)).ToList();
        public static List<long> ReadSplitLong => ReadLine().Split().Select(s => long.Parse(s)).ToList();
        public static List<double> ReadSplitdouble => ReadLine().Split().Select(s => double.Parse(s)).ToList();
        #endregion

        #region Output
        public static void OutJoinSpace<T>(IEnumerable<T> list) => WriteLine(string.Join(" ", list));
        #endregion
    }
}

Compiler output:
main.c:1:1: error: unknown type name 'using'
    1 | using System;
      | ^~~~~
main.c:2:1: error: unknown type name 'using'
    2 | using System.Collections.Generic;
      | ^~~~~
main.c:2:13: error: expected '=', ',', ';', 'asm' or '__attribute__' before '.' token
    2 | using System.Collections.Generic;
      |             ^
main.c:3:1: error: unknown type name 'using'
    3 | using System.Linq;
      | ^~~~~
main.c:3:13: error: expected '=', ',', ';', 'asm' or '__attribute__' before '.' token
    3 | using System.Linq;
      |             ^
main.c:4:1: error: unknown type name 'using'
    4 | using System.Text;
      | ^~~~~
main.c:4:13: error: expected '=', ',', ';', 'asm' or '__attribute__' before '.' token
    4 | using System.Text;
      |             ^
main.c:5:6: error: expected ';' before 'static'
    5 | using static System.Console;
      |      ^~~~~~~
      |      ;
main.c:5:20: error: expected '=', ',', ';', 'asm' or '__attribute__' before '.' token
    5 | using static System.Console;
      |                    ^
main.c:6:6: error: expected ';' before 'static'
    6 | using static System.Math;
      |      ^~~~~~~
      |      ;
main.c:6:20: error: expected '=', ',', ';', 'asm' or '__attribute__' before '.' token
    6 | using static System.Math;
      |                    ^
main.c:8:1: error: unknown type name 'namespace'
    8 | namespace Atcoder
      | ^~~~~~~~~
main.c:9:1: error: expected '=', ',', ';', 'asm' or '__attribute__' before '{' token
    9 | {
      | ^
main.c:44:10: error: invalid preprocessing directive #region
   44 |         #region Input
      |          ^~~~~~
main.c:54:10: error: invalid preprocessing directive #endregion
   54 |         #endregion
      |          ^~~~~~~~~
main.c:56:10: error: invalid preprocessing directive #region
   56 |         #region Output
      |          ^~~~~~
main.c:58:10: error: invalid preprocessing directive #endregion
   58 |         #endregion
      |          ^~~~~~~~~