import java.util.*;
public class Main{
public static void main(String[] args){
Scanner in = new Scanner(System.in);
while(in.hasNext()){
String s1 = in.next();
String s2 = in.next();
String s = s1 + s2;
StringBuffer sb1 = new StringBuffer();
StringBuffer sb2 = new StringBuffer();
for(int i=0;i<s.length();i++){
if(i%2==0){
sb1.append(s.charAt(i));
}else{
sb2.append(s.charAt(i));
}
}
char[] chs1 = sb1.toString().toCharArray();
char[] chs2 = sb2.toString().toCharArray();
Arrays.sort(chs1);
Arrays.sort(chs2);
char [] cha = new char[chs1.length+chs2.length];
int j = 0, k = 0;
for (int i=0; i<cha.length; i++)
{
if (i%2 == 0)
{
cha = chs1[j];
j++;
}
else
{
cha = chs2[k];
k++;
}
}
for (int i=0; i<cha.length; i++)
{
cha = change(cha);
}
System.out.println(cha);
}
in.close();
}
// 不明觉厉
public static char change(char a) {
char res;
switch (a) {
case '0': res='0';break;
case '1': res='8';break;
case '2': res='4';break;
case '3': res='C';break;
case '4': res='2';break;
case '5': res='A';break;
case '6': res='6';break;
case '7': res='E';break;
case '8': res='1';break;
case '9': res='9';break;
case 'A': res='5';break;
case 'B': res='D';break;
case 'C': res='3';break;
case 'D': res='B';break;
case 'E': res='7';break;
case 'F': res='F';break;
case 'a': res='5';break;
case 'b': res='D';break;
case 'c': res='3';break;
case 'd': res='B';break;
case 'e': res='7';break;
case 'f': res='F';break;
default :res=a;
}
return res;
}