public class Main {

    public static void main(String[] args) {

        System.out.println(getEvenDigitSum(1221)); 

        // output is 4

    }

    public static int getEvenDigitSum (int number) {

        if (number >= 0) {

            int sum = 0;

            int lastDigit = 0;

            while (number > 0) {

                if ((number % 2) == 0) {

                    lastDigit = number % 10;

                    sum += lastDigit;

                }

                number /= 10;

            }

            return sum;

        } else {

            return -1;

        }

    }

}