O=C1OC(c2ccc(O)c(-c3ccccc3)c2)(c2ccc(O)c(-c3ccccc3)c2)c2c(Cl)c(Cl)c(Cl)c(Cl)c21
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?