#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;
using ll = long long;

int main(){

    string S;
    cin >> S;
    int cnt=1;
    for (auto x : S) if (x == 'a') cnt++;

    cout << string(cnt, 'a') << endl;

    return 0;
}