function change(name) {
    
    var pic_before_change;
    
    pic_before_change = document.images[name].src;
	
    check_pic = pic_before_change.substr(pic_before_change.length-6, 2);	
	    
    if(check_pic=="-a"){
	document.images[name].src=pic_before_change.substring(0, pic_before_change.length-6)+".gif";
    }
    else{
	document.images[name].src=pic_before_change.substring(0, pic_before_change.length-4)+"-a.gif";
    }
}