@Contract(pure = true)
  public static int rankForFileSize(long fileSize) {
    if (fileSize < 0) throw new IllegalArgumentException("Invalid value: " + fileSize);
    return (int)((Math.log10(fileSize) + 0.0000021714778384307465) / 3);  // (3 - Math.log10(999.995))
  }
@Contract(pure = true)
  public static int rankForFileSize(long fileSize)