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.*;
import java.math.BigInteger;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.*;
import javafx.beans.binding.StringBinding;

public class Main {

    static final int INF = Integer.MAX_VALUE;

    static void mergeSort(int[] a, int p, int r) {
        if (p < r) {
            int q = (p + r) / 2;
            mergeSort(a, p, q);
            mergeSort(a, q + 1, r);
            merge(a, p, q, r);
        }
    }

    static void merge(int[] a, int p, int q, int r) {
        int n1 = q - p + 1;
        int n2 = r - q;
        int[] L = new int[n1 + 1], R = new int[n2 + 1];
        // int[] L1 = new int[n1 + 1], R1 = new int[n2 + 1];

        for (int i = 0; i < n1; i++) {
            L[i] = a[p + i];
            //  L1[i] = b[p + i];

        }
        for (int i = 0; i < n2; i++) {
            R[i] = a[q + 1 + i];
            // R1[i] = b[q + 1 + i];

        }
        L[n1] = R[n2] = INF;
        // L1[n1] = R1[n2] = INF;

        for (int k = p, i = 0, j = 0; k <= r; k++) {
            if (L[i] <= R[j]) {

                a[k] = L[i++];
                //  b[k] = L1[i++];

            } else {
                a[k] = R[j++];
                // b[k] = R1[j++];

            }
        }
    }

    static void mergeSort(int[] a, int[] b, int p, int r) {
        if (p < r) {
            int q = (p + r) / 2;
            mergeSort(a, b, p, q);
            mergeSort(a, b, q + 1, r);
            merge(a, b, p, q, r);
        }
    }

    static void merge(int[] a, int[] b, int p, int q, int r) {
        int n1 = q - p + 1;
        int n2 = r - q;
        int[] L = new int[n1 + 1], R = new int[n2 + 1];
        int[] L1 = new int[n1 + 1], R1 = new int[n2 + 1];
        // int[] L2 = new int[n1 + 1], R2 = new int[n2 + 1];

        for (int i = 0; i < n1; i++) {
            L[i] = a[p + i];
            L1[i] = b[p + i];
            // L2[i] = a[p + i];
        }
        for (int i = 0; i < n2; i++) {
            R[i] = a[q + 1 + i];
            R1[i] = b[q + 1 + i];
            //  R2[i] = a[q + 1 + i];
        }
        L[n1] = R[n2] = INF;
        L1[n1] = R1[n2] = INF;
        // L2[n1] = R2[n2] = INF;

        for (int k = p, i = 0, j = 0; k <= r; k++) {
            if (L[i] <= R[j]) {
                a[k] = L[i];
                b[k] = L1[i++];
                // c[k] = L2[i++];
            } else {
                a[k] = R[j];
                b[k] = R1[j++];
                // c[k] = R2[j++];
            }
        }
    }

    public static int[] sieve(int n) {
        int a[] = new int[n + 1];
        for (int i = 2; i <= n; i++) {
            a[i] = 1;
        }
        for (int i = 2; i <= Math.sqrt(n); i++) {
            if (a[i] == 1) {
                for (int k = 2; i * k <= n; k++) {
                    a[i * k] = 0;
                }
            }
        }
        return a;
    }

    public static long sum(int a) {
        long su = 0;
        while (a > 0) {
            su += (long) a % 10;
            a /= 10;
        }
        return su;
    }

    public static int divi(int b) {
        int n = 0;
        for (int i = 2; i <= Math.sqrt(b); i++) {
            if (b % i == 0) {
                n = i;
                break;
            }
        }
        if (n == 0) {
            return b;
        }
        return n;
    }

    public static boolean prime(int n) {
        if (n == 1) {
            return true;
        }

        for (int i = 2; i <= Math.sqrt(n); i++) {
            if (n % i == 0) {
                return false;
            }
        }
        return true;
    }

    public static String reve(int a, int b, String s) {
        String q = "";
        for (int i = b; i >= a; i--) {
            q += s.charAt(i);
        }
        return q;
    }

    public static boolean isvowel(char c) {
        if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u' || c == 'y') {
            return true;
        } else {
            return false;
        }
    }

    static long gcd(long a, long b) {
        return b == 0 ? a : gcd(b, a % b);
    }

    public static int hole(int n) {
        int y = 0;
        if (n == 1) {
            return 0;
        }
        if (prime(n)) {
            return 1;
        }
        for (int i = 2; i <= Math.sqrt(n); i++) {
            if (n % i == 0) {
                if (prime(i)) {
                    y++;
                }
                if (prime(n / i) && i != (n / i)) {
                    y++;
                }
            }
        }
        return y;
    }

    static List<Integer> gd(int a, int b) {
        int m = (int) gcd(a, b);
        List<Integer> q = new ArrayList();
        for (int i = 1; i * i <= m; ++i) {
            if (m % i == 0) {
                q.add(i);
                if (i != m / i) {
                    q.add(m / i);
                }
            }
        }
        return q;
    }

    static boolean contain(int[] a) {
        for (int i = 1; i < a.length; i++) {
            if (a[i] == 0) {
                return true;
            }
        }
        return false;
    }

    static void decrease(int[] a) {
        for (int i = 1; i < a.length; i++) {
            a[i]--;
        }
    }

    static long power(StringBuilder s) {
        long c = 1, sum = 0;
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == 'C') {
                c *= 2;
            } else {
                sum += c;
            }
        }
        return sum;
    }

    static long sum(long n) {
        return n * (n + 1) / 2;
    }

    static int divisors(int n) {
        Set<Integer> c = new HashSet();
        for (int i = 1; i <= Math.sqrt(n); i++) {
            if (n % i == 0) {
                c.add(i);
                c.add((int) (n / i));
            }
        }
        return c.size();
    }

    static boolean cal(int val, int k, int t) {
        int res = val, p = 1;
        while (val / Math.pow(k, p) > 0) {
            res += val / Math.pow(k, p);
            p++;
        }
        return res >= t;
    }

    static int Last_Ocuu(long[] a, int n,long v) {
        int start = 0, end = n-1, mid,ans=-1;

        while (start <= end) {
            mid = (start + end) >> 1;
            if (a[mid]>v) {
                ans=mid;
                end=mid-1;
            }
            else if (a[mid]<v) {
                //ans=mid;
                start=mid+1;
            }
            else return mid;

        }
        return ans;
    }

    static void print(int a, String s) {

        if (a > 0) {
            //s+='*';
            System.out.println(s);
            print(a - 1, '*' + s);
        } else {
            return;
        }
    }

    static long max(int[] a) {

        long m = 0;
        int max = a[a.length - 1];
        for (int i = a.length - 1; i > 0; i--) {
            if (a[i] == a[i - 1]) {
                m++;
            }
        }
        if (m == 0) {
            m++;
        }
        return m;
    }

    static int summtion(int[] a) {
        int s = 0;
        for (int i = 0; i < a.length; i++) {
            s += a[i];
        }
        return s;
    }
    static boolean vv(int i,int j,int n,int m){
        if (i>=0&&i<n&&j<m&&j>=0) {
            return true;
        }
        return false;
    }
    static  boolean valid(char [] []a,int i,int j,int n,int m){
        char k=a[i][j];
        if (Character.isDigit(k)) {
            int co=0;
            if (vv(i, j+1, n, m)) {//
                if(a[i][j+1]=='*')co++;
            }
            if (vv(i+1, j, n, m)) {//
                if(a[i+1][j]=='*')co++;
            }
            if (vv(i+1, j+1, n, m)) {//
                if(a[i+1][j+1]=='*')co++;
            }
            if (vv(i-1, j, n, m)) {//
                if(a[i-1][j]=='*')co++;
            }
            if (vv(i, j-1, n, m)) {//
                if(a[i][j-1]=='*')co++;
            }
            if (vv(i-1, j-1, n, m)) {//
                if(a[i-1][j-1]=='*')co++;
            }
            if (vv(i-1, j+1, n, m)) {
                if(a[i-1][j+1]=='*')co++;
            }
            if (vv(i+1, j-1, n, m)) {
                if(a[i+1][j-1]=='*')co++;
            }
            if (co==Integer.parseInt(k+"")) {
                return true;
            }
            return false;
        }
        else if (k=='.') {
            if (vv(i, j+1, n, m)) {//
                if(a[i][j+1]=='*')return false;
            }
            if (vv(i+1, j, n, m)) {//
                if(a[i+1][j]=='*')return false;
            }
            if (vv(i+1, j+1, n, m)) {//
                if(a[i+1][j+1]=='*')return false;
            }
            if (vv(i-1, j, n, m)) {//
                if(a[i-1][j]=='*')return false;
            }
            if (vv(i, j-1, n, m)) {//
                if(a[i][j-1]=='*')return false;
            }
            if (vv(i-1, j-1, n, m)) {//
                if(a[i-1][j-1]=='*')return false;
            }
            if (vv(i-1, j+1, n, m)) {
                if(a[i-1][j+1]=='*')return false;
            }
            if (vv(i+1, j-1, n, m)) {
                if(a[i+1][j-1]=='*')return false;
            }
           
            
        }
         return true;
    }
    public static void main(String[] args) throws IOException, ParseException {
        Scanner in = new Scanner(System.in);
        PrintWriter or = new PrintWriter(System.out);
       char[] p= in.nextLine().toCharArray();
       char[] t= in.nextLine().toCharArray();
       StringBuilder s= new StringBuilder();
       
       int c=0;
        for (int i = 0; i < p.length; i++) {
            if(p[i]!=t[i])c++;
        }
        if (c%2==1) {
            or.println("impossible");
        }
        else if(c==0)or.println(new String(p));
        else{
            c= c>>1;
            int i;
            
            for ( i = 0; c>0; i++) {
                s.append(t[i]);
                if(p[i]!=t[i])c--;
            }
            for (; i <p.length; i++) {
                s.append(p[i]);
            }
            or.print(s);
        }
       
       
     or.flush();
    
    }
    static class Scanner {

        StringTokenizer st;
        BufferedReader br;

        public Scanner(FileReader fileReader) throws FileNotFoundException {
            br = new BufferedReader(fileReader);
        }

        public Scanner(InputStream s) throws FileNotFoundException {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
            return st.nextToken();
        }

        public double nextDouble() throws IOException {
            String x = next();
            StringBuilder sb = new StringBuilder("0");
            double res = 0, f = 1;
            boolean dec = false, neg = false;
            int start = 0;
            if (x.charAt(0) == '-') {
                neg = true;
                start++;
            }
            for (int i = start; i < x.length(); i++) {
                if (x.charAt(i) == '.') {
                    res = Long.parseLong(sb.toString());
                    sb = new StringBuilder("0");
                    dec = true;
                } else {
                    sb.append(x.charAt(i));
                    if (dec) {
                        f *= 10;
                    }
                }
            }
            res += Long.parseLong(sb.toString()) / f;
            return res * (neg ? -1 : 1);
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        public long nextLong() throws IOException {
            return Long.parseLong(next());
        }

        public String nextLine() throws IOException {
            return br.readLine();
        }

        public boolean ready() throws IOException {
            return br.ready();
        }

    }

}

class Pair implements Comparable<Pair> {

    int ind;
    int val;

    public Pair(int n, int p) {
        ind = n;
        val = p;
    }

    @Override
    public int compareTo(Pair o) {
        if (o.val == val) {
            return -1 * (o.ind - ind);
        }
        return (val - o.val);
    }

}