#include <bits/stdc++.h>
using namespace std;

int main() {
    string a, b;
    cin >> a >> b;
    vector<int> counts1(26);
    vector<int> counts2(26);
    for(char x : a) counts1[x-'a']++;
    for(char x : b) counts2[x-'a']++;
    for(int i = 0; i < 26; i++) for(int j = 0; j < max(counts1[i], counts2[i]); j++) cout << (char)('a'+i);
    cout << "\n";
}