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

using ll = long long;
#define fi first
#define se second

int main(){
    string s;
    cin>>s;
    int counta=0;
    for(int i=0;i<s.size();i++){
        if(s[i]=='a'){
            counta++;
        }
    }
    for(int i=0;i<counta+1;i++){
        cout<<'a';
    }
    cout<<endl;
}