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

public class Main {
public static Scanner input = new Scanner(System.in);

    public static void main(String[] args) {

        String inputStr = "";
        inputStr = input.nextLine();

        ArrayList arr = new ArrayList();
        String numberStr = "";
        int number = 0;
        int result = -1;
        boolean isFirst = false;

        for (int i = 0; i < inputStr.length(); i++) {

            if(Character.isDigit(inputStr.charAt(i))) {
                numberStr += String.valueOf(inputStr.charAt(i));
                isFirst = true;
            } else if(isFirst) {
                    number = Integer.parseInt(numberStr);
                    numberStr = "";
                    if(number % 2 == 0 && number > result) {
                        result = number;
                    }
                    isFirst = false;
            }
        }

        System.out.println(result);





    }
}