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:
//package codeforcesround.year2015.may.round303;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;
 
public class EquidistantString {
        BufferedReader br;
        PrintWriter out;
        StringTokenizer tk;
        boolean submit;
        
        private String ntk() { 
                while (tk == null || !tk.hasMoreTokens()) {
                        try {
                                tk = new StringTokenizer(br.readLine());
                        } catch (IOException e) {
                                return null;
                        }
                }
                return tk.nextToken();
        }
 
        private String nln() {
                try {
                        return br.readLine();
                } catch (IOException e) {
                        return null;
                }
        }
        
        private String ns() { 
                return ntk(); 
        }
 
        private int ni() throws IOException {
                return Integer.parseInt(ntk());
        }
        
        private long nl() throws IOException {
                return Long.parseLong(ntk());
        }
        
        private float nf() throws IOException {
                return Float.parseFloat(ntk());
        }
        
        private double nd() throws IOException {
                return Double.parseDouble(ntk());
        }
        
        private void debug(Object... o) {
                if(!submit) {
                        System.out.println(Arrays.deepToString(o));
                }
        }
 
        public static void main(String args[]) throws IOException {
                new EquidistantString();
        }
        
        public EquidistantString() throws IOException {
                long start = System.currentTimeMillis();
                submit = !false;
                if(submit == false) br = new BufferedReader(new InputStreamReader(new FileInputStream("D:\\input.txt")));
                else br = new BufferedReader(new InputStreamReader(System.in));
                out = new PrintWriter(System.out);
                
                NL = (int) (1e5 + 10);
                int t = 1; 
                while(t-- > 0)
                        solve();
                
                long end = System.currentTimeMillis();
                debug(end - start, " ms");
                out.close();
        }
        
        int N, NL;
        String S, T;
        StringBuilder P;
        private void solve() throws IOException {
                S = ns();
                T = ns();
                P = new StringBuilder();
                N = S.length();
                int distance = 0;
                for(int i = 0; i < N; i++) {
                        if(S.charAt(i) != T.charAt(i))
                                distance++;
                }
                if(distance % 2 != 0) {
                        out.println("impossible");
                        return;
                }
                boolean copyS = true;
                for(int i = 0; i < N; i++) {
                        if(S.charAt(i) != T.charAt(i)) {
                                if(copyS) {
                                        P.append(S.charAt(i));
                                } else {
                                        P.append(T.charAt(i));
                                }
                                copyS = !copyS;
                        } else {
                                P.append(S.charAt(i));
                        }
                }
                out.println(P.toString());
        }
}