#include <bits/stdc++.h>
using namespace std;
#define int long long
using vec_int = vector<int>;
using vec_ii = vector<vec_int>;
using vec_iii = vector<vec_ii>;
using vec_iiii = vector<vec_iii>;
using P = pair<int,int>;
using T = tuple<int,int,int>;
using ll = long long;
using ld = long double;
#define rep(i, n) for(int i = 0; i < (int)(n); i++)

void cout_line(vector<int> &a){
    for(int i=0;i<a.size();i++){
        if(i<a.size()-1){
            cout<<a.at(i)<<" ";
        }else{
            cout<<a.at(i)<<endl;
        }
    }
}

int charToInt(char c){
    char zero_num = '0';
    return (int)c - (int)zero_num;
}

signed main(){
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    string S; cin>>S;
    int num = 0;
    rep(i, S.size()){
        if(S.at(i)=='a')num++;
    }
    string ans = "";
    rep(i, num+1) ans += 'a';
    cout<<ans<<endl;





    return 0;
}