What is the highest population for the province having a rank under 5?
CREATE TABLE "demography" (
  "year" real,
  "population" real,
  "five_year_pct_change" text,
  "ten_year_pct_change" text,
  "rank_among_provinces" real
);
SELECT MAX("population") FROM "demography" WHERE "rank_among_provinces"<5;