var image_dir = "images/";
var ImageNum = 0;
var TotalNum = 0;

imageArray = new Array();
imageArray[ImageNum++] = image_dir + "galbum21_1.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_4.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_5.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_7.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_8.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_9.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_10.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_11.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_12.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_13.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_16.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_18.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_19.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_26.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_28.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_31.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_32.jpg";
imageArray[ImageNum++] = image_dir + "galbum21_33.jpg";

TotalNum = ImageNum;
ImageNum = -1;

function AvanzaImage()
{
   ImageNum++;
   if (ImageNum == TotalNum)
     ImageNum=0;
   document.mainimage.src = imageArray[ImageNum];
}

function RetrocedeImage()
{
   ImageNum--;
   if (ImageNum == -1)
     ImageNum= TotalNum - 1;
   document.mainimage.src = imageArray[ImageNum];
}