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.PrintWriter;
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Array;
import java.math.BigInteger;
import java.text.DecimalFormat;
import java.util.*;

import static java.lang.Math.max;
import static java.lang.Math.min;

/* Built using CHelper plug-in
*/
public class codeforces{
    static class pair implements Comparable<pair> {
        int a, b;


        public pair(int a, int b) {
            this.a = a;
            this.b = b;
        }

        //@Override
        @Override
        public int compareTo(pair p) {
            return this.b - p.b;
        }
    }
    static class x {
        String a, b;
        public x(String a, String b) {
            this.a = a;
            this.b = b;
        }
    }
    static  FastReader in;
    static PrintWriter out;
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        in = new FastReader(inputStream);
        out = new PrintWriter(outputStream);
        Ques solver;
        solver = new Ques();
        //int testNumber=in.nextInt();
        //while(testNumber-->0)
        solver.solve(1, in, out);
        out.flush();
        out.close();
    }
    static class Ques {
        public void solve(int testNumber, FastReader in, PrintWriter out){
            String i = ns();
            String j = ns();
            int n = i.length();
            StringBuilder output = new StringBuilder();
            int count = 0;
            for(int a = 0; a < n; a++){
                if(i.charAt(a) == j.charAt(a)){
                    output.append(i.charAt(a));
                }
                else{
                    count++;
                    if(count%2 == 0){
                        output.append(i.charAt(a));
                    }
                    else{
                        output.append(j.charAt(a));
                    }
                }
            }
            if(count%2 == 0){
                System.out.println(output);
            }
            else{
                System.out.println("impossible");
            }

        }
        private static int ni(){
            return in.nextInt();
        }
        private static long nl(){
            return in.nextLong();
        }
        private static String ns(){
            return in.nextString();
        }
        private static char nc(){
            return in.nextCharacter();
        }
        private static double nd(){
            return in.nextDouble();
        }

        private static char[] ns(int n) {
            char[] a = new char[n];
            for(int i=0;i<n;i++) a[i] = nc();
            return a;
        }

        private static char[][] nm(int n, int m)
        {
            char[][] map = new char[n][];
            for(int i=0;i<n;i++) map[i] = ns(m);
            return map;
        }

        private static int[] na(int n)
        {
            int[] a = new int[n];
            for(int i=0;i<n;i++) a[i] = ni();
            return a;
        }

        private static long[] nal(int n)
        {
            long[] a = new long[n];
            for(int i=0;i<n;i++) a[i] = nl();
            return a;
        }
    }
    static long lcm(long a, long b) { return (a * (b / GCD(a, b))); }
    static long  infinity=Long.MAX_VALUE;
    public static int[] radixSort(int[] f){ return radixSort(f, f.length); }
    public static int[] radixSort(int[] f, int n) {
        int[] to = new int[n];
        {
            int[] b = new int[65537];
            for(int i = 0;i < n;i++)b[1+(f[i]&0xffff)]++;
            for(int i = 1;i <= 65536;i++)b[i]+=b[i-1];
            for(int i = 0;i < n;i++)to[b[f[i]&0xffff]++] = f[i];
            int[] d = f; f = to;to = d;
        }
        {
            int[] b = new int[65537];
            for(int i = 0;i < n;i++)b[1+(f[i]>>>16)]++;
            for(int i = 1;i <= 65536;i++)b[i]+=b[i-1];
            for(int i = 0;i < n;i++)to[b[f[i]>>>16]++] = f[i];
            int[] d = f; f = to;to = d;
           }
        return f;
    }
    static final int MAXN = 1000001;
    // stores smallest prime factor for every number
    static int spf[] = new int[MAXN];
    // Calculating SPF (Smallest Prime Factor) for every
    // number till MAXN.
    // Time Complexity : O(nloglogn)
    static void sieve() {
        spf[1] = 1;
        for (int i=2; i<MAXN; i++)

            // marking smallest prime factor for every
            // number to be itself.
            spf[i] = i;

        // separately marking spf for every even
        // number as 2
        for (int i=4; i<MAXN; i+=2)
            spf[i] = 2;

        for (int i=3; i*i<MAXN; i++)
        {
            // checking if i is prime
            if (spf[i] == i)
            {
                // marking SPF for all numbers divisible by i
                for (int j=i*i; j<MAXN; j+=i)

                    // marking spf[j] if it is not
                    // previously marked
                    if (spf[j]==j)
                        spf[j] = i;
            }
        }
    }

    // A O(log n) function returning primefactorization
    // by dividing by smallest prime factor at every step
    static Vector<Integer> getFactorization(int x)
    {
        Vector<Integer> ret = new Vector<>();
        while (x != 1&&spf[x]!=0)
        {
            ret.add(spf[x]);
            x = x / spf[x];
        }
        return ret;
    }
    static long GCD(long a, long b) { return (a%b == 0)? Math.abs(b) : GCD(b,a%b); }
    static long ncr(long n,long r){
        if(r==0 || r==n) return 1;
        double d=1;
        if(r>n) r=n-r;
        for(int i=0;i<r;i++){
            d*=(double)(n-i)/(i+1);
        }
        return (long)d;
    }
    static long d, x, y;
    static void extendedEuclid(long A, long B) {
        if(B == 0) {
            d = A;
            x = 1;
            y = 0;
        }
        else {
            extendedEuclid(B, A%B);
            long temp = x;
            x = y;
            y = temp - (A/B)*y;
        }
    }
    static long modInverse(long A, long M)
    {
        extendedEuclid(A,M);
        return (x%M+M)%M;
    }
    static long modPow(long x,long y,long M){
        if(y==0) return 1;
        if(y%2==0) return modPow((x*x)%M,y/2,M);
        else return (x*modPow((x*x)%M,(y-1)/2,M))%M;
    }
    static long M = (long) Math.pow(10,9)+7;
    static long fact(long x){
        if(x==0 || x==1) return 1;
        return ((x%M) * (fact(x-1)%M))%M;
    }
    static long power(long x,long y){
        if(y==0) return 1;
        if(y%2==0) return power((x*x)%M,y/2)%M;
        else return (x*power((x*x)%M,(y-1)/2))%M;
    }
    static class FastReader {
        private InputStream stream;
        private byte[] buf = new byte[8192];
        private int curChar;
        private int pnumChars;
        private FastReader.SpaceCharFilter filter;

        public FastReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {
            if (pnumChars == -1) {
                throw new InputMismatchException();
            }
            if (curChar >= pnumChars) {
                curChar = 0;
                try {
                    pnumChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (pnumChars <= 0) {
                    return -1;
                }
            }
            return buf[curChar++];
        }
        private String readLine0(){
            StringBuilder buf = new StringBuilder ();
            int c = read ();
            while (c != '\n' && c != -1){
                if (c != '\r'){
                    buf.appendCodePoint (c);
                }
                c = read ();
            }
            return buf.toString ();
        }
        public String nextLine(){
            String s = readLine0 ();
            while (s.trim ().length () == 0)
                s = readLine0 ();
            return s;
        }
        public String nextLine(boolean ignoreEmptyLines){
            if (ignoreEmptyLines){
                return nextLine ();
            }else{
                return readLine0 ();
            }
        }
        public char nextCharacter(){
            int c = read ();
            while (isSpaceChar (c))
                c = read ();
            return (char) c;
        }

        public double nextDouble(){
            int c = read ();
            while (isSpaceChar (c))
                c = read ();
            int sgn = 1;
            if (c == '-'){
                sgn = -1;
                c = read ();
            }
            double res = 0;
            while (!isSpaceChar (c) && c != '.'){
                if (c == 'e' || c == 'E'){
                    return res * Math.pow (10, nextInt ());
                }
                if (c < '0' || c > '9'){
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read ();
            }
            if (c == '.'){
                c = read ();
                double m = 1;
                while (!isSpaceChar (c)){
                    if (c == 'e' || c == 'E'){
                        return res * Math.pow (10, nextInt ());
                    }
                    if (c < '0' || c > '9'){
                        throw new InputMismatchException ();
                    }
                    m /= 10;
                    res += (c - '0') * m;
                    c = read ();
                }
            }
            return res * sgn;
        }

        public int nextInt() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                if (c == ',') {
                    c = read();
                }
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }
        public String next() {
            return nextString();
        }
        public int[] nextIntArray(int n) {
            int a[] = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }
        public long nextLong() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }
        public String nextString() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }
        public BigInteger nextBigInteger(){
            try{
                return new BigInteger (nextString());
            } catch (NumberFormatException e){
                throw new InputMismatchException ();
            }
        }

        public boolean isSpaceChar(int c) {
            if (filter != null) {
                return filter.isSpaceChar(c);
            }
            return isWhitespace(c);
        }

        public static boolean isWhitespace(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);

        }


    }
}