function nextImage(cartoonnum){
	if(photonum<maxphotonum){
		photonum++;
		changeImage(photonum,cartoonnum);
	}else{
		window.open(official_url,"_blank");
	}
}

 function prevImage(cartoonnum){
 	if(photonum!=1){
		photonum--;
		changeImage(photonum,cartoonnum);
	}
}

function changeImage(num,cartoonnum){
	document.mainimage.src='http://www.yoasobitai.net/contents/cartoon/'+cartoonnum+"/"+num+".jpg";
}