Problem: 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 si isn't equal to ti. 

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.

Input

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 105. It is guaranteed that both strings contain only digits zero and one.

Output

Print a string of length n, consisting of digits zero and one, that meets the problem statement. If no such string exist, print on a single line "impossible" (without the quotes).

If there are multiple possible answers, print any of them.

Examples

Input

0001
1011


Output

0011


Input

000
111


Output

impossible

Note

In the first sample different answers are possible, namely — 0010, 0011, 0110, 0111, 1000, 1001, 1100, 1101.

Solution (in JAVA):

Solution:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import static java.lang.Math.*;
import java.util.*;
import java.io.PrintStream;
import java.io.PrintWriter;
 
public class A {
 
	static final int mod = 1000000007;
	static final long MOD = 1000000007;
	static final int temp = 998244353;
	static final long M = (int)1e9+7;
 
	
	static class Pair implements Comparable<Pair>
	{
		long first, second;
		public Pair(long aa, long bb)
		{
			first = aa; second = bb;
		}
		public int compareTo(Pair p)
		{
//			if(a == p.a) return b - p.b;
//			return a - p.a;
			if(first == p.first) return (int)(second - p.second);
			return (int)(first - p.first);
		}
	}
	
	/*
	 * IO FOR 2D GRID IN JAVA
	 * char[][] arr = new char[n][m]; //grid in Q.
			
			for(int i = 0;i<n;i++)
			{
				char[] nowLine = sc.next().toCharArray();
				for(int j = 0;j<m;j++)
				{
					arr[i][j] = nowLine[i];
				}
			}
	 * */
	
	static void sort(int[] a) {
		ArrayList<Integer> l=new ArrayList<>();
		for (int i:a) l.add(i);
		Collections.sort(l);
		for (int i=0; i<a.length; i++) a[i]=l.get(i);
	}
	
	static class Reader {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String next() {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}
		
		int nextInt() {
			return Integer.parseInt(next());
		}
		int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) a[i]=nextInt();
			return a;
		}
		
		long[] longReadArray(int n) throws IOException {
			long[] a=new long[n];
			for (int i=0; i<n; i++) a[i]=nextLong();
			return a;
		}
		
		long nextLong() {
			return Long.parseLong(next());
		}
		double nextDouble() {
			return Double.parseDouble(next());
		}
	}
	
 
	public static boolean isPrime(long n) {
		if(n == 1)
		{
			return false;
		}
		for(long i = 2;i*i<=n;i++)
		{
			if(n%i == 0)
			{
				return false;
			}
		}
		return true;
	}
	
	public static List<Integer> Sieve(int n)
	{
		boolean prime[] = new boolean[n+1];
		Arrays.fill(prime, true);
		List<Integer> l = new ArrayList<>();
		
		
		for (int p=2; p*p<=n; p++) 
		{ 
			if (prime[p] == true) 
			{ 	
			    for(int i=p*p; i<=n; i += p) 
				{
				    prime[i] = false; 
				}	
			} 
		} 
 
		for (int p=2; p<=n; p++) 
		{
		    if (prime[p] == true)
		    {
		       l.add(p); 
		    }
		}
		
		return l;
	}
	
	
	public static int gcd(int a, int b)
	{
		if(b == 0)
		 return a;
		
		else
		return gcd(b,a%b);
	}
	
	public static long LongGCD(long a, long b)
	{
		if(b == 0)
			 return a;
			
			else
			return LongGCD(b,a%b);
	}
 
 
	public static int lcm(int a, int b)
    {
        return (a / gcd(a, b)) * b;
    }
	
	public static int phi(int n)  //euler totient function
    { 
        int result = 1; 
        for (int i = 2; i < n; i++) 
            if (gcd(i, n) == 1) 
                result++; 
        return result; 
    }
	
	    
	public static int[] computePrefix(int arr[], int n)
	{
		int[] prefix = new int[n];
		prefix[0] = arr[0];
		for(int i = 1;i<n;i++)
		{
			prefix[i] = prefix[i-1]+arr[i];
		}
		
		return prefix;
	}
	
	
	public static long fastPow(long x, long n) //include mod at each step if asked and in args of fn too
	{
		if(n == 0)
			return 1;
		else if(n%2 == 0)
			return fastPow(x*x,n/2);
		else
			return x*fastPow(x*x,(n-1)/2);
	}
	
	
	   public static long power(long x, long y, long p)
	    {
	 
	        long res = 1;
	 
	        x = x % p;
	 
	        while (y > 0) {
	            if (y % 2 == 1)
	                res = (res * x) % p;
	 
	            y = y >> 1; 
	            x = (x * x) % p;
	        }
	 
	        return res;
	    }
	   
	   static long modInverse(long n, long p)
	    {
	        return power(n, p - 2, p);
	    }
	 
	    // Returns nCr % p using Fermat's little theorem.
	    
	    public static long nCr(long n, long r,
	                             long p)
	    {
	          if (n<r) 
	              return 0;
	          
	        if (r == 0)
	            return 1;
	 
	        long[] fac = new long[(int)(n) + 1];
	        fac[0] = 1;
	 
	        for (int i = 1; i <= n; i++)
	            fac[i] = fac[i - 1] * i % p;
	 
	        return (fac[(int)(n)] * modInverse(fac[(int)(r)], p)
	                % p * modInverse(fac[(int)(n - r)], p)
	                % p)
	            % p;
	    }
	    
	    public static long[] modInvArr(long n, long mod)
	    {
	    	long[] ans = new long[(int)(n)+1];
			ans[1] = 1;
			for(int i = 2;i <= n;i++)
			{
				ans[i] = (mod - (mod/i) * ans[(int)(mod%i)])%mod;
			}
			return ans;
	    }
 
		public static int LowerBound(int a[], int x) {
			  int l=-1,r=a.length;
			  while(l+1<r) {
			    int m=(l+r)>>>1;
			    if(a[m]>=x) r=m;
			    else l=m;
			  }
			  return r;
			}
		
		
		public static int UpperBound(int a[], int x) {
		    int l=-1;
		    int r=a.length;
		    while(l+1<r) {
		       int m=(l+r)>>>1;
		       if(a[m]<=x) l=m;
		       else r=m;
		    }
		    return l+1;
		}
		
		public static void Sort(int[] a) {
			List<Integer> l=new ArrayList<>();
			for (int i:a) l.add(i);
			Collections.sort(l);
			//Collections.reverse(l);  //Use to Sort decreasingly 
			for (int i=0; i<a.length; i++) a[i]=l.get(i);
		}
		
		//MODULO OPS for addition and multiplication 
		
		   public static long perfomMod(long x){
		        return ((x%M + M)%M);
		    }
		   public static long addMod(long a, long  b){
		        return perfomMod(perfomMod(a)+perfomMod(b));
		    }
		   public static long mulMod(long  a, long b){
		        return perfomMod(perfomMod(a)*perfomMod(b));
		   }
	
		
	public static void main(String[] args) throws IOException 
	{
		Reader sc=new Reader();
		PrintWriter out = new PrintWriter(System.out);

		char[] a = sc.next().toCharArray();
		char[] b = sc.next().toCharArray();
		int diff=  0, c = 0, n = a.length;
		for(int i = 0;i<n;i++)
		{
			if(a[i] != b[i])
			{
				diff++;
			}
		}
		
		if(diff % 2 == 1)
		{
			System.out.println("impossible");
			return;
		}
		
		String ans = "";
		int count = 0;
		for(int i = 0;i<n;i++)
		{
			if(a[i] == b[i])
			{
				ans += a[i];
				continue;
			}
			if(count > 0)
			{
				ans += b[i];
			}
			else {
				ans  += a[i];
			}
			
			count = count ^ 1;
		}
		
		System.out.println(ans);
		out.close();
	}
 
	
}