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.
def distance(a,b):
    rast = 0
    for i in range(len(a)):
        if a[i] != b[i]:
            rast += 1
    return rast

def ravn(a,b):
    while len(a) < len(b):
        a = '0'+a
    return a

a = '000'
b = '111'
i = 0
a1 = ''
try:
    while len(a1)<=len(a):
        i+=1
        a1 = bin(i)
        a1 = a1.replace('0b','')
        a1 = ravn(a1,b)
        if distance(a1,a) == distance(a1,b):
            print(a)
            break
except:
    print('impossible')