I back <apostrophe>s of his months .
(ROOT_0 (S_0 (ATS_3 (ATS_1 (NP_1 (PRP_0 I)) (ADVP_0 (RB_0 back))) (VP_3 (VBZ_0 <apostrophe>s) (PP_1 (IN_1 of) (NP_0 (PRPDOLLAR_0 his) (NNS_0 months))))) (DOT_0 .)))