import java.util.*;

public class Puppy {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String word1 = scanner.nextLine();
        String word2 = scanner.nextLine();

        String newWord = "";

        int length = Math.min(word1.length(), word2.length());
        int differenceBetweenSizes = Math.abs(word1.length() - word2.length());

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

            int x = word1.charAt(i) - 'a';
            int y = word2.charAt(i) - 'a';

            if (x == -65 || y == -65) {
                newWord += " ";
                continue;
            }

            int result = Math.abs(x - y) + 'a';

            char join = (char) result;

            newWord += join;
        }

        for (int i = differenceBetweenSizes; i > 0; i--) {

            if (word1.length() < word2.length()) {

                newWord += word2.charAt(word2.length() - i);
            }
        }

        System.out.println(newWord);
    }
}