import java.io.*;
import java.util.*;

class Main
{
    public static void main(String args[])throws Exception
    {
        BufferedReader bu=new BufferedReader(new InputStreamReader(System.in));
        StringBuilder sb=new StringBuilder();
        String s=bu.readLine();
        int i,n=s.length(),a=1;
        for(i=0;i<n;i++)
        if(s.charAt(i)=='a') a++;

        while(a-->0) sb.append('a');
        System.out.println(sb);
    }
}