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); } }