615 B | 615 chars
import sys
from math import sqrt, pi, sin, factorial
inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = " " : [*map(int,inp().split(x))]
mfi = lambda x = " " : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
while 1:
a = inp()
if a == "0":
break
b = inp()
ans = ""
for i in range(len(b)):
y = ord(b[i]) - 64
x = ord(a[i % len(a)]) - 64
ans += chr((x + y + 25) % 26 + 65)
p(ans)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()