#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main(){
string str, str1, str2;
string a("0123456789abcdefABCDEF");
string b("084C2A6E195D3B7F5D3B7F");
cin >> str1 >> str2;
str = str1 + str2;
str1.clear(); str2.clear();
for(int i = 0; i < str.size(); ++i)
if(i % 2 == 0)
str1 += str[i];
else
str2 += str[i];
sort(str1.begin(), str1.end());
sort(str2.begin(), str2.end());
for(int i = 0; i < str.size(); ++i)
if(i % 2 == 0)
str[i] = str1[i/2];
else
str[i] = str2[(i-1)/2];
for(int i = 0; i < str.size(); ++i){
int n = a.find_first_of(str[i]);
if(n != -1)
str[i] = b[n];
}
cout << str;
}