#include <bits/stdc++.h>
#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
#include <iomanip>
#include<set>
#include <numeric>
#include<string>
using ll = long long;
using namespace std;

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