# Arup Guha
# 11/23/2024
# Drunk Vigenere (on Kattis)
# https://open.kattis.com/problems/drunkvigenere

# Get key and cipher.
cipher = input().strip()
key = input().strip()

# Loop through and do it!
sign = -1
for i in range(len(cipher)):

    # Get answer.
    let1 = ord(cipher[i])-ord('A')
    let2 = ord(key[i])-ord('A')

    # Calculate answer.
    ans = (let1 + sign*let2+26)%26

    # Convert and print.
    print(chr(ans+ord('A')), end="")

    # Flip flop...
    sign = -sign