Pokemon Don’t Go

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

namespace _09._PokemonDon_tGo
{
    class Program
    {
        static void Main(string[] args)
        {
            List<int> numbers = Console.ReadLine()
                .Split(" ", StringSplitOptions.RemoveEmptyEntries)
                .Select(int.Parse)
                .ToList();

            List<int> numsToSum = new List<int>(numbers.Count);

            while (numbers.Count > 0)
            {
                int index = int.Parse(Console.ReadLine());

                bool? isInSequence = CheckIndex(index, numbers);

                SwapElements(numbers, isInSequence);

                if (numbers.Count > 0)
                {
                    index = ChangeIndex(index, isInSequence, numbers.Count);

                    RemovePokemon(numbers, index, numsToSum);
                }

            }

            Console.WriteLine(numsToSum.Sum());
        }

        private static void RemovePokemon(List<int> numbers, int index, List<int> numsToSum)
        {
            // 1. make temp
            int temp = numbers[index];
            // 2. Remove numbers[index]
            numbers.RemoveAt(index);
            // 3. Add temp to sumList
            numsToSum.Add(temp);

            for (int i = 0; i < numbers.Count; i++)
            {
                // 4.1 increase value of smaller elements
                if (numbers[i] <= temp)
                {
                    numbers[i] += temp;
                }
                // 4.2 decrease value of greater elements
                else
                {
                    numbers[i] -= temp;
                }
            }
        }

        private static int ChangeIndex(int index, bool? isInSequence, int lenght)
        {
            if (isInSequence == false)
            {
                return 0;
            }
            else if (isInSequence == null)
            {
                return lenght - 1;
            }
            else
            {
                return index;
            }
        }

        private static void SwapElements(List<int> numbers, bool? isInSequence)
        {
            if (isInSequence == false)
            {
                int temp = numbers[numbers.Count-1];
                // 1. Remove first Element
                numbers.RemoveAt(0);
                // 2. Copy last element to index[0]
                numbers.Insert(0, numbers[numbers.Count-1]);
            }
            else if (isInSequence == null)
            {
                int temp = numbers[0];
                // 1. Remove last Element
                numbers.RemoveAt(numbers.Count - 1);
                // 2. Copy first element to index[last]
                numbers.Add(temp);
                numbers.Add(temp);
            }
        }

        private static bool? CheckIndex(int index, List<int> numbers)
        {
            if (index < 0)
            {
                return false;
            }
            else if (index >= numbers.Count)
            {
                return null;
            }
            else
            {
                return true;
            }
        }
    }
}