# 1 将输入的两个字符串进行合并
ls = input().split(" ")
s = ls[0] + ls[1]

s1 = sorted(s[0::2])
s2 = sorted(s[1::2])

# 2 下标分奇偶分别排序
ns = ""
for i in range(len(s)):
    if i % 2 == 0:
        ns += s1[i // 2]
    else:
        ns += s2[i // 2]

# 数制转换
rs = ""
for i in ns:
    if i.isdigit() or ord("a") <= ord(i.lower()) and ord(i.lower()) <= ord("f"):

        a1 = int(i, 16)
        a2 = (bin(a1)[2:].zfill(4))[::-1]
        a3 = int(a2, 2)
        a4 = (hex(a3)[2:]).upper()
        rs += a4
    else:
        rs += i
print(rs)