C# HackerRank, 10 Days of Statistics, Day 1: Quartiles

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

namespace Quartiles
{
    class Program
    {
        private static List<int> numbers = new List<int>();
        private static List<int> lowerQuartile = new List<int>();
        private static List<int> upperQuartile = new List<int>();

        private static string[] STDIN_Numbers;

        private static int numberOfElements = 0;

        static void Main(string[] args)
        {
            numberOfElements = Convert.ToInt32(Console.ReadLine()); // User input - number of elements
            STDIN_Numbers = Console.ReadLine().Split(' '); // User input - single spaced element list
            PrepareList();
            PrepareQuartiles();

            Console.WriteLine($"{IntMedian(lowerQuartile)}");
            Console.WriteLine($"{IntMedian(numbers)}");
            Console.WriteLine($"{IntMedian(upperQuartile)}");
        }

        private static void PrepareList() // Prepare main numbers list since user input is string type and list require int type
        {
            int outputNumber;
            for (int i = 0; i < STDIN_Numbers.Length; i++) // Populate numbers list from user input.
            {
                if(!int.TryParse(STDIN_Numbers[i], out outputNumber)) // Check if input is a number and convert it to int
                {
                    Console.WriteLine("Error: Input parameter is not an integral number.");
                }
                numbers.Add(outputNumber); // Add converted and checked elements to list
            }

            numbers.Sort(); // Sort list ascending
        }

        private static void PrepareQuartiles() // Split main list into lower and upper quartile lists
        {
            // notEvenSection is used in not even amount of elements or as first element in even amount.
            // evenSection is used only for even amount of elements.
            int notEvenSection = numbers.Count / 2;
            int evenSection = (numbers.Count / 2) - 1;

            if (IsEven(numbers.Count)) // Check if element list is even
            {
                for (int i = 0; i <= evenSection; i++) // Populate lower quartile list
                {
                    lowerQuartile.Add(numbers[i]);
                }
                for (int i = notEvenSection; i < numbers.Count; i++) // Populate upper quartile list
                {
                    upperQuartile.Add(numbers[i]);
                }
            }
            else // Run if list in odd
            {
                for (int i = 0; i < notEvenSection; i++) // Populate lower quartile list
                {
                    lowerQuartile.Add(numbers[i]);
                }
                for (int i = notEvenSection + 1; i < numbers.Count; i++) // Populate upper quartile list
                {
                    upperQuartile.Add(numbers[i]);
                }
            }
        }

        private static int IntMedian(List<int> _list) // Calculate median in integral list
        {
            int firstSection = _list.Count / 2;
            int secondSection = (_list.Count / 2) - 1;

            if (IsEven(_list.Count)) // Return median from even list
            {
                return (_list.ElementAt(firstSection) + _list.ElementAt(secondSection)) / 2;
            }
            else // Return median from odd list
            {
                return _list.ElementAt(firstSection);
            }
        }

        private static bool IsEven(int _arg) // Check if number is even or odd, return true if even. General helper.
        {
            if (_arg % 2 == 0)
                return true;
            else
                return false;
        }
    }
}