public String lowestSlot() {
   BigInteger lowest = BigInteger.ZERO;
   JSONArray json = getJSON();
   boolean passed = false;
   while (!passed) {
     passed = true;
     for (int i = 0; i < json.length(); i++) {
       JSONObject o = json.getJSONObject(i);
       BigInteger current = o.getBigInteger("slot");
       if (current.compareTo(lowest) == 0) {
         lowest = lowest.add(BigInteger.ONE);
         passed = false;
         break;
       }
     }
   }
   return lowest.toString();
 }