#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using pint = pair<int, int>;
using pll = pair<ll, ll>;

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