function getLastValue(itemId){

   var cache = CacheService.getPublicCache();
   var cached = cache.get(itemId.toString());

   if (cached != null) {
     return cached;
   } else {

     var json =ImportJSON("http://services.runescape.com/m=itemdb_rs/api/graph/" + itemId + ".json", "/daily");
     var daily = json[json.length - 1];

     cache.put(itemId.toString(), daily[daily.length - 1], 14400); // cache for 4 hours

     return daily[daily.length - 1];
   }
}