function change(num, speed, pic1, pic2) {
      var i= num % pic2 + pic1;
      var j= ((num+1) % pic2) + pic1;
      $("#img"+ i).fadeOut(2000);
      $("#img"+ j).fadeIn(2000);
      setTimeout("change("+j+", "+speed+", "+ pic1+", "+pic2+")", speed);
}