Name the total number of panelists for 19 january 2007
CREATE TABLE "series_4" (
  "episode_number" real,
  "air_date" text,
  "guest_host" text,
  "musical_guest_song_performed" text,
  "who_knows_the_most_about_the_guest_host_panelists" text,
  "coat_of_cash_wearing_celebrity" text
);
SELECT COUNT("who_knows_the_most_about_the_guest_host_panelists") FROM "series_4" WHERE "air_date"='19 January 2007';