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 girl(s, t):
    distance = 0
    ls = len(s)
    mas_dif = []
    for i in range(ls):
        if s[i] != t[i]:
            mas_dif.append(i)
            distance += 1
    if distance%2!=0:
        print("impossible")
        return 0

    else:
        new_str = ""
        chet = True
        for i in range(len(s)):
            if i in mas_dif:
                if chet:
                    new_str += s[i]
                    chet = False
                else:
                    new_str += t[i]
                    chet = True
            else: new_str += s[i]
        print(new_str)
        return 0


s = input()
t = input()
girl(s, t)
