What is the gdp of the country with an area of 83871 (km2)?
CREATE TABLE "1995_enlargement" (
  "member_countries" text,
  "population" real,
  "area_km" real,
  "gdp_billion_us" text,
  "gdp_per_capita_us" real
);
SELECT "gdp_billion_us" FROM "1995_enlargement" WHERE "area_km"=83871;