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

imageArray = new Array();
imageArray[ImageNum++] = image_dir + "gsantalucia_1.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_2.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_3.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_4.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_5.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_6.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_7.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_8.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_9.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_10.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_11.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_12.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_13.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_14.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_15.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_16.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_17.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_18.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_19.jpg";
imageArray[ImageNum++] = image_dir + "gsantalucia_20.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];
}