Name the total number of series sorted for when released is april 2010
CREATE TABLE "series_1" (
  "num" real,
  "series_sorted" text,
  "title" text,
  "author" text,
  "doctor" text,
  "featuring" text,
  "released" text
);
SELECT COUNT("series_sorted") FROM "series_1" WHERE "released"='April 2010';