var v:array[1..1000000]of char;
    ordo:boolean;i,n,j:longint;aux:char;
begin
assign(input,'ordine.in');reset(input);
assign(output,'ordine.out');rewrite(output);
i:=0;
while not eof do begin
    inc(i);
    read(v[i]);
    end;
n:=i;
repeat
ordo:=true;
for i:=1 to n-1 do
    if v[i]>v[i+1]then begin
       ordo:=false;
       aux:=v[i];
       v[i]:=v[i+1];
       v[i+1]:=aux;
       end;
until ordo;
for i:=1 to n-1 do
    if v[i]=v[i+1] then
       if i<n-1 then begin
          j:=i+2; ordo:=false;
          repeat
            if v[i+1]<>v[j] then begin
               aux:=v[i+1];
               v[i+1]:=v[j];
               v[j]:=aux;
               ordo:=true
               end;
          inc(j);
          until ordo;
    end;
for i:=1 to n do write(v[i]);
end.