bcdef
abbbc
 z
y
 reddit
abcdef
 abc
aaa
 y
z
 cbxz
aaaa

bccdb
 z
 dfdeed
 aab
 y
 abac

from sys import *
f = lambda: sorted(stdin.readline()[:-1])
t = [f()[::-1], f()]
n = len(t[0])
p = [n & 1, 1]
s = ''
for i in range(n):
    k = t[0][-1] < t[1][-1]
    p[k] ^= 1
    s += t[p[k]].pop()
print(s)