What is the sum of Year with a Type of informal, and a Location with justus lipsius building, brussels, and a Date with 23 may?
CREATE TABLE table_54598 (
    "Year" real,
    "Date" text,
    "Type" text,
    "President" text,
    "Location" text
)
SELECT SUM("Year") FROM table_54598 WHERE "Type" = 'informal' AND "Location" = 'justus lipsius building, brussels' AND "Date" = '23 may'
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 of Year with a Type of informal, and a Location with justus lipsius building, brussels, and a Date with 23 may? ### Input: CREATE TABLE table_54598 (
    "Year" real,
    "Date" text,
    "Type" text,
    "President" text,
    "Location" text
) ### Response: SELECT SUM("Year") FROM table_54598 WHERE "Type" = 'informal' AND "Location" = 'justus lipsius building, brussels' AND "Date" = '23 may'