What is the title when 18.58 u.s. viewers  (millions) watched?
CREATE TABLE "table1_18217741_1" (
  "series_num" real,
  "season_num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "u_s_viewers_millions" text
);
SELECT "title" FROM "table1_18217741_1" WHERE "u_s_viewers_millions"='18.58';