function showMainPic(nr) {

	src = document.getElementById("menu_sub_pic_" + nr).src;
	len = src.length;
	ext = src.substring(len,len-3);
	clr = src.substring(len,len-9);
		
	if ((ext=="jpg" || ext=="gif" || ext=="png") && clr !="clear.gif") {
		strArr = src.split(".");
		mainPic = strArr[0];
		
			
		for(i=1;i<strArr.length-1;i++) {
			mainPic = mainPic + "." + strArr[i];
		}
		mainPic = mainPic + "gross." + strArr[i];
		document.getElementById("mainpic").src = mainPic; 
		document.getElementById("menu_sub_pic_link_" + nr).className = "menupic active";
		for(i=1;i<4;i++) {
			if(i==nr) {
				document.getElementById("menu_sub_pic_link_" + nr).className = "menupic active";
			} else {
				src = document.getElementById("menu_sub_pic_" + i).src;
				len = src.length;
				clr = src.substring(len,len-9);
				if(clr =="clear.gif") {
					document.getElementById("menu_sub_pic_link_" + i).className = "menupic not_active";
				} else {
					document.getElementById("menu_sub_pic_link_" + i).className = "menupic";
				}
			}
		}
	}
}