what is the prod.code of the episode with original air date 01/12/1968?
CREATE TABLE "table1_13403120_1" (
  "num" real,
  "title" text,
  "director" text,
  "writer_s" text,
  "originalairdate" text,
  "repeatairdate_s" text,
  "prod_code" text
);
SELECT COUNT("prod_code") FROM "table1_13403120_1" WHERE "originalairdate"='01/12/1968';