#include <iostream>
#include <string>

using namespace std;
int main()
{
	string S;
	cin >> S;
	string S1;
	int num = 0;
	for (int i = 0; i < S.size(); i++) {
		if (S[i] == 'a') {
			num++;
		}
	}
	for (int i = 0; i <= num; i++) {
		cout << 'a';
	}
	cout << endl;
	return 0;
}