var r,s:string;
    i,j,k:longint;
begin
readln(s);
assign(input,'ordine.in'); reset(input);
assign(output,'ordine.out'); rewrite(output);
 for i:=97 to 122 do
  for j:=1 to length(s) do begin
   if i=ord(s[j]) then begin
    inc(k);
    r[k]:=chr(ord(i));
   end;
  end;
  for i:=1 to k do write(r[i]);
 close(input); close(output);
end.