What is the total number of modern grannies performed?
CREATE TABLE "series_1_round_summary_top_24" (
  "name_name_of_act" text,
  "age_s" text,
  "genre" text,
  "act" text,
  "hometown" text,
  "semifinal_week" real,
  "position_reached" text
);
SELECT COUNT("act") FROM "series_1_round_summary_top_24" WHERE "name_name_of_act"='Modern Grannies';