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


int main() {
    string S,out;
    cin >> S;
    int cnt;
    cnt = 0;
    out = "a";
    for (int i=0;i<S.length();i++){
        if (S[i] == 'a'){
            out += "a";
        }
    }
    cout << out << endl;
}