C[C@@H](C(=O)N1CCN(C(=O)OC(C)(C)C)CC1)n1cc(-c2cn([C@@H](C)C(=O)N3CCN(C(=O)OC(C)(C)C)CC3)nn2)nn1
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.