Why Wring answer?
import java.util.Scanner;

public class T1654 {
    public static char[] arr;
    public static String out = "";
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner sc = new Scanner(System.in);
        String inp = sc.next();
        sc.close();
        arr = new char[inp.length()];
        arr = inp.toCharArray();
        format();
        if(out != "") {
            System.out.println(out);
        } else {
            System.out.println("");
        }

    }

    public static void format() {
        boolean isFormat = false;
        int l = arr.length;
        for(int i = 0; i< l-1; i++) {
            if(arr[i] == arr[i+1]) {
                arr[i] = 0;
                arr[i+1] = 0;
                isFormat = true;
                } else if(arr[i] != arr[i+1] & arr[i] != 0){
                out += arr[i];
            }
        }
        out+= arr[arr.length-1];
        if(isFormat == true) {
            arr = new char[out.length()];
            arr = out.toCharArray();
            out = "";
            format();
        }
    }

}