O=C1C[C@H](CCC(=O)OCc2ccccc2)NC(=O)C[C@H](CCC(=O)OCc2ccccc2)NC(=O)C[C@H](CCC(=O)OCc2ccccc2)N1
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?