O=S(=O)(O)c1ccc2c(c1)-c1nc-2nc2[nH]c(nc3nc(nc4[nH]c(n1)c1ccc(S(=O)(=O)O)cc41)-c1ccc(S(=O)(=O)O)cc1-3)c1ccc(S(=O)(=O)O)cc21
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?