program ordine2;
var fin,fout:text;
    cuv,cuv2:string;
    min,aux:char;
    i,k,poz,lungime:byte;
    sch:boolean;
begin
assign(fin,'ordine.in');reset(fin);
readln(fin,cuv);close(fin);lungime:=length(cuv);
repeat
sch:=false;
for i:=1 to length(cuv)-1 do
 if cuv[i]>cuv[i+1]then
  begin aux:=cuv[i];
        cuv[i]:=cuv[i+1];
        cuv[i+1]:=aux;
        sch:=true
  end;
until not(sch);
i:=1;k:=1;
cuv2:=cuv[1];cuv:=copy(cuv,2,length(cuv)-1);
repeat
if cuv[i]<>cuv2[k] then begin cuv2:=cuv2+cuv[i];inc(k);
                              cuv:=copy(cuv,1,i-1)+copy(cuv,i+1,length(cuv)-i);
                              i:=1;
                        end
                   else inc(i);
until k=lungime;
assign(fout,'ordine.out');rewrite(fout);
write(fout,cuv2);close(fout);
end.