using System;

public class Program

{

    public static void Main()

    {

        //Approach:Call recursion to remove all adjacent matching characters

        string str1 = "ABCCCBCBA";

        Program prg = new Program();

        Console.WriteLine("String output after removing all matching characters: " + prg.RemoveDuplicateAdjChars(str1));            

    }

    private string RemoveDuplicateAdjChars(string str){

        string outstr = string.Empty;

        int len = str.Length;

        //Console.WriteLine(len);

        char[] arr = str.ToCharArray();

        if (len > 1){

            for(int i = 0; i< len; i++){

                //Condition to add last element of the array

                if(i == len - 1){

                    outstr += arr[i];

                    //Console.WriteLine(outstr);

                }

                //Append all non matching characters

                else if(arr[i] != arr[i+1]){

                    outstr += arr[i];

                }

                //Skip all matching characters by just moving the pointer index forward

                else if(arr[i] == arr[i+1]){

                    //Console.WriteLine(i);

                    while(arr[i] == arr[i+1]){

                        i++;

                        //Console.WriteLine(i);

                    }

                }

            }

            Console.WriteLine("Output string after removal method is called: " + outstr);

        }

        Program prg = new Program();

        //Call the method again till the output string is similar to input string

        if(str != outstr){

            outstr = prg.RemoveDuplicateAdjChars(outstr);

        }

        return outstr;

    }

}