import java.util.List;
import java.util.ArrayList;
import java.util.Scanner;


public class Spion {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        List<String>shifr = new ArrayList();
        String word = in.next();

    shifr.add(""+word.charAt(0));

    for(int i =1;i<word.length();i++){
        String s =""+word.charAt(i);
        shifr.add(s);

        if(shifr.get(shifr.lastIndexOf(s)).equals(shifr.get(shifr.indexOf(s))) && shifr.lastIndexOf(s)==shifr.indexOf(s)+1)
            {
            shifr.remove(shifr.get(shifr.lastIndexOf(s)));
            shifr.remove(shifr.get(shifr.indexOf(s)));

            };

    }

        for(String n: shifr){

            System.out.print(n);
        }







    }

}

what's wrong?