What year is the happy planet index?
CREATE TABLE table_77747 (
    "Index" text,
    "Organization" text,
    "Year" real,
    "Rank" text,
    "Out of" real
)
SELECT SUM("Year") FROM table_77747 WHERE "Index" = 'happy planet index'
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: What year is the happy planet index? ### Input: CREATE TABLE table_77747 (
    "Index" text,
    "Organization" text,
    "Year" real,
    "Rank" text,
    "Out of" real
) ### Response: SELECT SUM("Year") FROM table_77747 WHERE "Index" = 'happy planet index'