it just works...

import java.util.*;
public class Test3 {


    public static void main(String[] args) {
        Scanner reader = new Scanner(System.in);
        String input = reader.nextLine();
        maxeven(input);
    }

    public static void maxeven(String input) {
        int currentEven;
        StringBuffer inputBuffer = new StringBuffer();
        int max=-1;
        ArrayList<Integer> myList = new ArrayList<>();

        for (int i = 0; i <input.length() ; i++) {
            if(String.valueOf(input.charAt(i)).equals("0")||
                    String.valueOf(input.charAt(i)).equals("1")||
                    String.valueOf(input.charAt(i)).equals("2")||
                    String.valueOf(input.charAt(i)).equals("3")||
                    String.valueOf(input.charAt(i)).equals("4")||
                    String.valueOf(input.charAt(i)).equals("5")||
                    String.valueOf(input.charAt(i)).equals("6")||
                    String.valueOf(input.charAt(i)).equals("7")||
                    String.valueOf(input.charAt(i)).equals("8")||
                    String.valueOf(input.charAt(i)).equals("9")) {
                inputBuffer.append(input.charAt(i));
            } else {
                inputBuffer.toString().trim();
                if(inputBuffer.toString().isEmpty()){
                    continue;
                } else {
                    myList.add(Integer.parseInt(inputBuffer.toString()));
                    inputBuffer = new StringBuffer();
                }
            }
        }
        Collections.sort(myList, Collections.reverseOrder());
        for (int i = 0; i <myList.size() ; i++) {
            if(myList.get(i)%2==0){
                max = myList.get(i);
                break;
            } else {
                continue;
            }
        }
        System.out.println(max);
    }
}