// Arup Guha
// 11/23/2024
// Solution to Drunk Vigenere on Kattis

import java.util.*;

public class drunkvigenere {

	public static void main(String[] args) {
	
		// Get input.
		Scanner stdin = new Scanner(System.in);
		char[] cipher = stdin.next().toCharArray();
		char[] key = stdin.next().toCharArray();
		
		// Loop through letters.
		int sign = -1;
		for (int i=0; i<cipher.length; i++) {
			
			// Get int value of output.
			int val = ((cipher[i] - 'A') + sign*(key[i]-'A')+26)%26;
			
			// Convert and print.
			System.out.print((char)(val+'A'));
			sign = -sign;
		}
		System.out.println();
		
	}
}