using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Microsoft.VisualBasic;

namespace Reversing_and_Combining_Text
{
    class Program
    {
        static void Main(string[] args)
        {
            string text = "abc def ghi jkl";
            List<string> str= new List<string> { };
            List<string> str2 = new List<string> { };
            str = text.Split(' ').ToList();
            int n=str.Count();
            int k;
            char temp;
            int spaces = n - 1;
            while( n !=1)
            {

                for (int i = 0; i < n; i++)
                {
                    char[] arr = str[i].ToCharArray();
                    k = arr.Length;
                    for (int j = 0, h = k - 1; j < h; j++, h--)
                    {
                        temp = arr[j];
                        arr[j] = arr[h];
                        arr[h] = temp;
                    }
                    str[i] = String.Concat(arr);
                    arr = null;
                }
                for (int i = 0; i < n - 1; i++)
                {
                    str[i] += str[i + 1];
                }
                for (int i = 0; i < n; i++)
                {
                    if (i % 2 == 0)
                    {
                        str2.Add(str[i]);
                    }
                }
                str.Clear();
                for (int i = 0; i < str2.Count(); i++)
                {
                    str.Add(str2[i]);
                }
                str2.Clear();
                n = str.Count();
            }

            string newText = string.Concat<string>(str);
            Console.WriteLine(newText);
        }
    }
}