Observable<Transaction> myCatchUpToLatestAndSubscribeToNewTransactionsObservable(
  DefaultBlockParameter startBlock) {


  return web3j.catchUpToLatestAndSubscribeToNewBlocksObservable(startBlock, false)
    .flatMap(currentBlock -> {
      BigInteger confirmedBlock = currentBlock.getBlock().getNumber().subtract(confirmationBlock);
      return web3j.ethGetBlockByNumber(DefaultBlockParameter.valueOf(confirmedBlock), true).observable();
    }).flatMapIterable(MyWeb3j::toTransactions);
}