public long lastModified() {
   long lastModified = 0;
   for (int i = 0; ; i++) {
     FilePath f = getBase(i);
     if (f.exists()) {
       long l = f.lastModified();
       lastModified = Math.max(lastModified, l);
     } else {
       break;
     }
   }
   return lastModified;
 }