program sir;
var i,n:integer;
    a:char;
    ok:boolean;
    v:string;
begin
    readln(v);
    n:=length(v);
    ok:=true;
    while ok=true do
          begin
             ok:=false;
             for i:=1 to n-1 do
                 if ord(v[i])>ord(v[i+1]) then
                      begin
                         a:=v[i];
                         v[i]:=v[i+1];
                         v[i+1]:=a;
                         ok:=true;
                      end;
            end;
     ok:=true;
     while ok=true do
          begin
             ok:=false;
             for i:=1 to n-1 do
                 if ord(v[i])=ord(v[i+1]) then
                      begin
                         a:=v[i+1];
                         v[i+1]:=v[i+2];
                         v[i+2]:=a;
                         ok:=true;
                      end;
           end;
     for i:=1 to n+1 do
         write(v[i]);
end.