Fold and Sum

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

namespace test
{
    class MainClass
    {
        public static void Main()
        {

            int[] arr = Console.ReadLine()
                                 .Split(' ')
                                   .Select(int.Parse)
                                     .ToArray();

            var k = arr.Length / 4;

            int[] upper = new int[k * 2];
            int[] lower = new int[k * 2];

            int[] arrSum = new int[k * 2];


            for (int i = 0; i < k ; i++)
            {
                upper[i] = arr[k - 1 - i];
                upper[i + k] = arr[k * 4 - 1 - i];
            }

            for (int i = 0; i < k * 2; i++)
            {
                lower[i] = arr[k + i];
            }

            for (int i = 0; i < k * 2; i++)
            {
                arrSum[i] = upper[i] + lower[i];
            }

            Console.WriteLine(string.Join(" ", arrSum));
        }
    }
}