O=C1[C@H]2[C@@H](C(=O)N1C1CCCCC1)[C@@H](c1ccc(F)cc1)N1C(=O)N(c3ccccc3)C(=O)[C@@]21Cc1ccc(Cl)cc1
Heavy atom refers to any atom that is not hydrogen. The heavy atoms in molecules are carbon, oxygen, nitrogen, and sulfur. How many heavy atoms are in the molecule?