program NOD_SOFTWARE;
var v,x:array [1..1000000] of char;
    p,c:char;
    point,i,j,n,m,poz,indice:longint;
    fin,fout:text;
    ok:boolean;
{*-----------------------*}
function cautare(c:char):longint;
var i:integer;
begin
     cautare:=0;
     for i:=1 to n do if v[i] = c then
     begin
          cautare:=i;
          exit;
     end;
end;
{*-----------MAIN---------*}
begin
     assign(fin,'ordine.in'); reset(fin);
     assign(fout,'ordine.out'); rewrite(fout);
     n:=0;
     while not eoln(fin) do
     begin
          inc(n);
          read(fin,v[n]);
     end;
     indice:=0;

     for p:='a' to 'z' do
     begin
          ok:=true;
          while ((ok) and (cautare(p)>0)) do
          begin
               ok:=false;
               poz:=cautare(chr(ord(p)-1));
               if poz > 0 then
               begin
                    if x[indice] = p then
                    begin
                         inc(indice);
                         x[indice]:=v[poz];
                         inc(indice);
                         x[indice]:=p;
                    end
                    else
                    begin
                         inc(indice);
                         x[indice]:=p;
                         inc(indice);
                         x[indice]:=v[poz];
                    end;
                    ok:=true;
                    v[poz]:='$'
               end
               else
               begin
                    poz:=cautare(chr(ord(p)+1));
                    if poz > 0 then
                    begin
                         if x[indice] = p then
                         begin
                              inc(indice);
                              x[indice]:=v[poz];
                              inc(indice);
                              x[indice]:=p;
                         end
                         else
                         begin
                              inc(indice);
                              x[indice]:=p;
                              inc(indice);
                              x[indice]:=v[poz];
                         end;
                         v[poz]:='$';
                         ok:=true;
                    end;
               end;
               v[cautare(p)]:='$'
          end;
     end;
     for i:=1 to indice do write(fout,x[i]);
     close(fin);
     close(fout);

end.