O=C(O)CN(CC(=O)O)Cc1cc2c(-c3ccccc3C(=O)O)c3cc(CN(CC(=O)O)CC(=O)O)c(=O)cc-3oc2cc1O
PSA is a commonly used medicinal chemistry metric for the optimization of a drug's ability to permeate cells. Please predict psa of this molecule.