using System;

namespace pain
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = Console.ReadLine();

            char[] ss = new char[s.Length];

            for (int i = 0; i < s.Length; i++)
                ss[i] = s[i];
            for (int i = 0; i < s.Length - 1;)
            {

                if (ss[i] == ss[i + 1])
                {

                    if (i - 1 >= 0)
                    {
                        int n = i + 2;
                        b:
                        if (n <= s.Length - 1)
                        {
                            if (ss[n] != ' ')
                            {
                                ss[i] = ss[n];
                                ss[n] = ' ';
                                ss[i + 1] = ' ';
                            }
                            else
                            {
                                n++;
                                goto b;
                            }
                        }
                        else
                            break;

                    }
                    else
                    {
                        ss[i] = ' ';
                        ss[i + 1] = ' ';
                    }
                    if (i >= 1)
                        i--;
                    else
                        i++;

                }
                else
                    i++;
            }

            for (int i = 0; i < s.Length; i++)
                if(ss[i] != ' ')
                    Console.Write(ss[i]);

            //Console.Write(st2(s));
            Console.ReadLine();
        }

        public static string st1(string s, ref int n)
        {
            if (s.Length - 1 > n)
            {
                if (s[n] == s[n + 1])
                {
                    s = s.Remove(n, 2);
                    if (n >= 2)
                        n -= 2;
                    else
                        n--;
                }
                n++;
                s = st1(s, ref n);
            }
            return s;
        }
        public static string st2(string s)
        {
            for (int i = 0; i < s.Length - 1; i++)
            {
                if (s[i] == s[i + 1])
                {
                    s = s.Remove(i, 2);
                    if (i >= 2)
                        i -= 2;
                }
            }
            return s;
        }
        public static string st3(string s)
        {
            int n = 0;
            int nt = s.Length - 1;

            string[] ss = new string[nt];

            for (int i = 0; i < nt; i++)
            {
                bool d = false;
                for (int j = i; j < nt; j++)
                {
                    if (ss[i] == s[j].ToString())
                    {
                        d = true;
                    }
                }
                if (!d)
                {
                    ss[n] = s[i].ToString();
                    n++;
                }
            }

            n = 0;

            while (nt != 0)
            {
                nt = s.Length;
                for (int i = 0; i < ss.Length; i++)
                {
                    s = s.Replace(ss[i] + ss[i], "");
                }
                if (nt == s.Length)
                    break;
            }
            return s;
        }
    }
}

Edited by author 02.04.2019 03:06