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

string s;
int k = 0;

int main()
{
	cin >> s;

	for (int i = 0; i < s.size(); i++) {
		if (s[i] == 'a')
			k++;
	}

	for (int i = 0; i < k + 1; i++)
		cout << "a";

	cout << endl;
}