how many years did heartbeat series run in total ?
CREATE TABLE table_202_135 (
    id number,
    "series" number,
    "year" text,
    "rank" text,
    "average audience share" text
)
SELECT MAX("year") - MIN("year") FROM table_202_135
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: how many years did heartbeat series run in total ? ### Input: CREATE TABLE table_202_135 (
    id number,
    "series" number,
    "year" text,
    "rank" text,
    "average audience share" text
) ### Response: SELECT MAX("year") - MIN("year") FROM table_202_135