#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
using namespace std;

int main()
{
    string a,b;
    cin >> a >> b;

    sort(a.begin(), a.end());
    sort(b.begin(), b.end());

    string c;
    int s = -1;
    for(int i = 0, j = 0; i < sizeof(a) || j < sizeof(b);){
        if(s == -1 || (a[i] == b[j] && a[i] != c[s])){
            c+=a[i];
            s++;
        }
        else if(a[i] > b[j]){
            j++;
        }
        else{
            i++;
        }
    }
    cout << c;
    return 0;
}