List the number of vacators when successors were formally installed on June 22, 1868.
CREATE TABLE table_2417340_3 (
    vacator VARCHAR,
    date_of_successors_formal_installation VARCHAR
)
SELECT COUNT(vacator) FROM table_2417340_3 WHERE date_of_successors_formal_installation = "June 22, 1868"
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: List the number of vacators when successors were formally installed on June 22, 1868. ### Input: CREATE TABLE table_2417340_3 (
    vacator VARCHAR,
    date_of_successors_formal_installation VARCHAR
) ### Response: SELECT COUNT(vacator) FROM table_2417340_3 WHERE date_of_successors_formal_installation = "June 22, 1868"