#include<iostream>
#include<string>
using namespace std;

int main() {
    string s;
    cin >> s;
    int a = 0;
    for (int i = 0; i < (int)s.size(); i++) {
        if (s[i] == 'a') a++;
    }
    for (int i = 0; i <= a; i++) {
        cout << "a";
    }
    cout << endl;
}