The episode with the title "Written in Dust" is what episode #? 
CREATE TABLE "table1_26866233_1" (
  "series_num" real,
  "episode_num" real,
  "title" text,
  "director" text,
  "writer" text,
  "original_airdate" text
);
SELECT "episode_num" FROM "table1_26866233_1" WHERE "title"='\"Written in Dust\"';