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.
#define fi first
#define sec second
#include <bits/stdc++.h>
using namespace std;
int main (){
    string a,b;
    int c=0,d=0;
    cin>>a>>b;
    for (int i=0;i<a.size();i++){
        c=c+int(a[i]+b[i])-96;
    }
    if (c%2!=0){
        cout<<"impossible"<<endl;
        return 0;
    }
    for (int i=0;i<a.size();i++){
        if (d==0 && a[i]!=b[i]){
            cout<<b[i];
            d++;
        }
        else if (d==1&&a[i]!=b[i]){
            cout<<a[i];
            d--;
        }
        else {
            cout<<1
            ;
        }
    }
}
