SELECT MIN("GDP (billion US$)") FROM table_67871 WHERE "Population" > '54,292,038' AND "Area (km\u00b2)" > '30,528'
What is the GDP of the place with over 54,292,038 people and an Area (km ) greater than 30,528?
CREATE TABLE table_67871 (
    "Member countries" text,
    "Population" real,
    "Area (km\u00b2)" real,
    "GDP (billion US$)" real,
    "GDP per capita (US$)" text
)