What is the sum number of year when Call of Duty 4: Modern Warfare was the game?
CREATE TABLE table_name_55 (
    year VARCHAR,
    game VARCHAR
)
SELECT COUNT(year) FROM table_name_55 WHERE game = "call of duty 4: modern warfare"
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 is the sum number of year when Call of Duty 4: Modern Warfare was the game? ### Input: CREATE TABLE table_name_55 (
    year VARCHAR,
    game VARCHAR
) ### Response: SELECT COUNT(year) FROM table_name_55 WHERE game = "call of duty 4: modern warfare"