private static double totalSize(HLLCounter ... hs) {
    byte[] R = new byte[hs[0].getByteArray().length];
    for(int i = 0; i < hs.length; i++) {
      R = safeUnion(R, hs[i].getByteArray());
    }
    return estimateSize(R, getAlpha(R.length));
  }