Little Susie loves strings. Today she calculates distances between them. As Susie is a small girl after all, her strings contain only digits zero and one. She uses the definition of Hamming distance:

We will define the distance between two strings *s* and *t* of the same length consisting of digits zero and one as the number of positions *i*, such that *s*<sub class="lower-index">*i*</sub> isn't equal to *t*<sub class="lower-index">*i*</sub>. 

As besides everything else Susie loves symmetry, she wants to find for two strings *s* and *t* of length *n* such string *p* of length *n*, that the distance from *p* to *s* was equal to the distance from *p* to *t*.

It's time for Susie to go to bed, help her find such string *p* or state that it is impossible.
The first line contains string *s* of length *n*. 

The second line contains string *t* of length *n*.

The length of string *n* is within range from 1 to 10<sup class="upper-index">5</sup>. It is guaranteed that both strings contain only digits zero and one.
import sys, os, io
input = io.BytesIO(os.read(0, os.fstat(0).st_size)).readline

s = list(input().rstrip())
t = list(input().rstrip())
c = 0
for i, j in zip(s, t):
    c += i ^ j
if c % 2:
    ans = ["impossible"]
else:
    ans = [str(i & 1) for i in s]
    for i in range(len(s)):
        if not c:
            break
        if s[i] ^ t[i]:
            ans[i] = str(t[i] & 1)
            c -= 2
sys.stdout.write("".join(ans))