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

#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main() {
	string s;
	cin >> s;
	
	int n=s.size();
	
	int counter=1;
	
	rep(i,n){
		if (s[i]=='a') counter++;
	}
	
	string ans ="";
	
	rep(i,counter) ans+="a";
	
	cout << ans << endl;
}