ChetniChisla

import java.util.Scanner;

public class ChetniChisla {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String input = scanner.nextLine();

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

        // If no numbers print -1
        if (splitStrings[0].equals("")){
            System.out.println(-1);
            return;
        }

        int maxEven = -1;

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

            if (Integer.parseInt(splitStrings[i]) % 2 == 0 && Integer.parseInt(splitStrings[i]) > maxEven) {
                maxEven = Integer.parseInt(splitStrings[i]);
            }
        }


        if(maxEven==-1){
            System.out.println(-1);
        } else {System.out.println(maxEven);}

    }
}