What was the sum of Value ($M), when the Revenue ($M) was less than 307, the Team was Valencia, and the Rank was smaller than 19?
CREATE TABLE "2008_rankings" (
  "rank" real,
  "team" text,
  "country" text,
  "value_m" real,
  "debt_as_pctof_value" real,
  "pct_change_on_year" text,
  "revenue_m" real,
  "operating_income_m" real
);
SELECT SUM("value_m") FROM "2008_rankings" WHERE "revenue_m"<307 AND "team"='valencia' AND "rank"<19;