bcdef
abbbc
 z
y
 reddit
abcdef
 abc
aaa
 y
z
 cbxz
aaaa

bccdb
 z
 dfdeed
 aab
 y
 abac

import java.util.*;
import java.io.*; 
import java.text.DecimalFormat;

public class Main{
    final long mod = (int)1e9+7, IINF = (long)1e19;
    final int MAX = (int)1e6+1, MX = (int)1e7+1, INF = (int)1e9, root = 3;
    DecimalFormat df = new DecimalFormat("0.0000000000000");
    double eps = 1e-9, pi = 3.141592653589793238462643383279502884197169399375105820974944;
    FastReader in;
    PrintWriter out;
    static boolean multipleTC = false, memory = false;

    public static void main(String[] args) throws Exception{
        if(memory)new Thread(null, new Runnable() {public void run(){try{new Main().run();}catch(Exception e){e.printStackTrace();}}}, "1", 1 << 28).start();
        else new Main().run();
    }

    void run() throws Exception{
        in = new FastReader();
        out = new PrintWriter(System.out);
        for(int i = 1, t = (multipleTC)?ni():1; i<=t; i++)solve(i);
        out.flush();    
        out.close();
    }
    
    void solve(int TC)throws Exception{
        String s1 = n(), s2 = n();
        int n = s1.length(), A = 26;
        int[] f1 = new int[A], f2 = new int[A];
        for(int i = 0; i< n; i++){
            f1[s1.charAt(i)-'a']++;
            f2[s2.charAt(i)-'a']++;
        }
        int[] ans = new int[n];
        Arrays.fill(ans, -1);
        int l = 0, r = A-1;
        int move = 0;
        for(int i = 0; i< n; i++){
            while(l<A && f1[l]==0)l++;
            while(r>=0 && f2[r]==0)r--;
            if(l>=r)break;
            if(move==0){
                ans[i] = l;
                f1[l]--;
            }else{
                ans[i] = r;
                f2[r]--;
            }
            move^=1;
        }
        l = 0;r = A-1;
        for(int i = n-1; i>= 0 && ans[i]==-1; i--){
            while(r>=0 && f1[r]==0)r--;
            while(l<A && f2[l]==0)l++;
            if(move==0){
                ans[i] = r;
                f1[r]--;
            }else{
                ans[i] = l;
                f2[l]--;
            }
            move ^=1;
        }
        for(int i = 0; i< n; i++)p((char)('a'+ans[i]));
    }
    
    int[] reverse(int[] a){
        int[] o = new int[a.length];
        for(int i = 0; i< a.length; i++)o[i] = a[a.length-i-1];
        return o;   
    }

    int[] sort(int[] a){
        if(a.length==1)return a;
        int mid = a.length/2;
        int[] b = sort(Arrays.copyOfRange(a,0,mid)), c = sort(Arrays.copyOfRange(a,mid,a.length));
        for(int i = 0, j = 0, k = 0; i< a.length; i++){
            if(j<b.length && k<c.length){
                if(b[j]<c[k])a[i] = b[j++];
                else a[i] = c[k++];
            }else if(j<b.length)a[i] = b[j++];
            else a[i] = c[k++];
        }
        return a;
    }

    long[] sort(long[] a){
        if(a.length==1)return a;
        int mid = a.length/2;
        long[] b = sort(Arrays.copyOfRange(a,0,mid)), c = sort(Arrays.copyOfRange(a,mid,a.length));
        for(int i = 0, j = 0, k = 0; i< a.length; i++){
            if(j<b.length && k<c.length){
                if(b[j]<c[k])a[i] = b[j++];
                else a[i] = c[k++];
            }else if(j<b.length)a[i] = b[j++];
            else a[i] = c[k++];
        }
        return a;
    }

    long gcd(long a, long b){return (b==0)?a:gcd(b,a%b);}
    int gcd(int a, int b){return (b==0)?a:gcd(b,a%b);}
    int bitcount(long n){return (n==0)?0:(1+bitcount(n&(n-1)));}
    void p(Object o){out.print(o);}
    void pn(Object o){out.println(o);}
    void pni(Object o){out.println(o);out.flush();}
    String n(){return in.next();}
    String nln(){return in.nextLine();}
    int ni(){return Integer.parseInt(in.next());}
    long nl(){return Long.parseLong(in.next());}
    double nd(){return Double.parseDouble(in.next());}

    class FastReader{
        BufferedReader br;
        StringTokenizer st;
        public FastReader(){
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        public FastReader(String s) throws Exception{
            br = new BufferedReader(new FileReader(s));
        }

        String next(){
            while (st == null || !st.hasMoreElements()){
                try{
                    st = new StringTokenizer(br.readLine());
                }catch (IOException  e){
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        String nextLine(){
            String str = "";
            try{
                str = br.readLine();
            }catch (IOException e){
                e.printStackTrace();
            }   
            return str;
        }
    }
}      