Bit Flipper

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


class Program
{
    static void Main(string[] args)
    {
        UInt64 input = UInt64.Parse(Console.ReadLine());

        string represent = Convert.ToString((long)input, 2).PadLeft(64, '0');
        //Console.WriteLine(represent);
        char[] representation_array = represent.ToCharArray();

        for (int i = 0; i < representation_array.Length - 2; i++)
        {
            if (representation_array[i] == representation_array[i + 1] && representation_array[i + 1] == representation_array[i + 2])
            {
                if (representation_array[i] == '1')
                {
                    representation_array[i] = '0';
                    representation_array[i + 1] = '0';
                    representation_array[i + 2] = '0';
                }
                else if (representation_array[i] == '0')
                {
                    representation_array[i] = '1';
                    representation_array[i + 1] = '1';
                    representation_array[i + 2] = '1';
                }
                i += 2;
            }
        }
        string temp_repres = new string(representation_array);
        int lenth = temp_repres.Length;

        UInt64 result = Convert.ToUInt64(temp_repres, 2);
        Console.WriteLine(result);
    }
}