O=c1c2cc3c(=O)n4c(cc(-c5ccccc5)c5cc(Cl)ccc54)nc3cc2nc2cc(-c3ccccc3)c3cc(Cl)ccc3n12
Hydrogen bond acceptor is the chemical compound which contains the lone electron pairs that participate in the hydrogen bond formation. How many hydrogen bond acceptors does the molecule contain?