program z325;
var
  n, a, b: integer;
  c: boolean;
begin
  readln(n);
  c := true;
  while n>=10 do
  begin
    a := n mod 10;
    b := (n div 10) mod 10;
    if b >= a then
    begin
      c := false;
      break;
    end;
    n := n div 10;
  end;
  if c then
    writeln('yes')
  else
    writeln('no');
end.