import string
alpha = list(string.ascii_lowercase)
s1 = list(input())
s2 = list(input())
for i in range(len(s1)):
    key = alpha.index(s1[i]) + alpha.index(s2[i]) + 1
    if key < 25:
        print(alpha[key], end='')
    else:
        print(alpha[key - 26], end='')

646918c3f202dabcb6323d018a343af39322e13e
<mask token>

<mask token>
for i in range(len(s1)):
    key = alpha.index(s1[i]) + alpha.index(s2[i]) + 1
    if key < 25:
        print(alpha[key], end='')
    else:
        print(alpha[key - 26], end='')

<mask token>
alpha = list(string.ascii_lowercase)
s1 = list(input())
s2 = list(input())
for i in range(len(s1)):
    key = alpha.index(s1[i]) + alpha.index(s2[i]) + 1
    if key < 25:
        print(alpha[key], end='')
    else:
        print(alpha[key - 26], end='')

import string
alpha = list(string.ascii_lowercase)
s1 = list(input())
s2 = list(input())
for i in range(len(s1)):
    key = alpha.index(s1[i]) + alpha.index(s2[i]) + 1
    if key < 25:
        print(alpha[key], end='')
    else:
        print(alpha[key - 26], end='')
