What was the lowest lost entry for a team with fewer than 21 goals for?
CREATE TABLE "third_division_final_table" (
  "position" real,
  "team" text,
  "played" real,
  "drawn" real,
  "lost" real,
  "goals_for" real,
  "goals_against" real,
  "goal_difference" text,
  "points_1" text
);
SELECT MIN("lost") FROM "third_division_final_table" WHERE "goals_for"<21;