#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;
}