import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		char[] s = sc.next().toCharArray();
		sc.close();

		int cnt = 1;
		for (int i = 0; i < s.length; i++) {
			if (s[i] == 'a') {
				cnt++;
			}
		}
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < cnt; i++) {
			sb.append('a');
		}
		System.out.println(sb.toString());
	}
}