import java.util.Scanner;

public class EvenNumbers {
    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);

        String input = scanner.nextLine();

        input = input.replaceAll("[^-?0-9]+", " ").trim();
        String[] words = input.split(" ");

        if(input.equals("")){
            System.out.print(-1);
            return;
        }

        Long maxEvenNumber = Long.MIN_VALUE;

        long[] numbers = new long[words.length];
        for(int i = 0; i < words.length; i ++){
            numbers[i] = Integer.parseInt(words[i]);
            if(numbers[i] % 2 == 0){
                long evenNumber = numbers[i];
                if(evenNumber > maxEvenNumber){
                    maxEvenNumber = evenNumber;
                }
            }
        }
        System.out.println(maxEvenNumber);
    }
}