#include <iostream>
#include <string>
using namespace std;

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