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.
#include <iostream>
using namespace std;
string t,s;
int f,x,i;
int main() {
	cin>>s>>t;
	for(i=0;i<s.length();i++)
	{
		if(s[i]!=t[i])x++;
		if(x%2==0)s[i]=t[i];
	}
	if(x&1)
	cout<<"impossible";
	else
	cout<<s;
}