var v:array[1..100]of char;
    s:string;
    i,j:integer;
    f,g:text;
    aux:char;
begin
  assign(f,'ordine.in');
  reset(f);
  assign(g,'ordine.out');
  rewrite(g);
  readln(f,s);
  For i:=1 to length(s) do
      For j:=1 to i do
          if s[j]>s[i] then begin
                              aux:=s[i];
                              s[i]:=s[j];
                              s[j]:=aux;
                            end;
  For i:=2 to length(s)-1 do
      if s[i]=s[i-1] then begin
                              aux:=s[i];
                              s[i]:=s[i-2];
                              s[i-2]:=aux;
                            end
                     else if s[i]=s[i+1] then begin
                              aux:=s[i+1];
                              s[i+1]:=s[i+2];
                              s[i+2]:=aux;
                            end;
  Writeln(g,s);
  close(f);
  close(g);
end.