How many mixed doubles were there in the year that Olga Koseli won the women's singles?
CREATE TABLE "past_winners" (
  "year" real,
  "mens_singles" text,
  "womens_singles" text,
  "mens_doubles" text,
  "womens_doubles" text,
  "mixed_doubles" text
);
SELECT COUNT("mixed_doubles") FROM "past_winners" WHERE "womens_singles"='Olga Koseli';