sentences: (b) Notwithstanding subsection (a) of this section, in the case of any alien described in such subsection—
  (1) whose deportation was subsequent to a conviction for commission of [certain misdemeanors] or a felony [other than an aggravated felony], such alien shall be fined under title 18, or imprisoned not more than 10 years or both, or
  (2) whose deportation was subsequent to a conviction for an aggravated felony, such alien shall be fined under title 18, imprisoned not more than 20 years, or both.