// David Poeschl

import java.util.*;

public class CryptographyDavid 
{
	public static void main(String[] args)
	{		
		Scanner scan = new Scanner(System.in);
		String ciphertext = scan.next();
		String key = scan.next();
		scan.close();
		
		for (int i = 0; i < ciphertext.length(); i++)
		{
			char messageChar = (char) ('A' + ((int)(ciphertext.charAt(i) - 'A') - (int)(key.charAt(i) - 'A') + 26) % 26);
			System.out.print(messageChar);
			key += messageChar;
		}
		
		System.out.println();
	}
}