What is the  episode # when the guests were julie nixon eisenhower and david eisenhower?
CREATE TABLE "table1_25691838_12" (
  "episode_num" real,
  "the_w_rd" text,
  "guest" text,
  "introductory_phrase" text,
  "original_airdate" text,
  "production_code" real
);
SELECT MIN("episode_num") FROM "table1_25691838_12" WHERE "guest"='Julie Nixon Eisenhower and David Eisenhower';