Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_77 (year INTEGER, date VARCHAR, type VARCHAR, location VARCHAR)
### Question:
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?
### Answer:
SELECT SUM(year) FROM table_name_77 WHERE type = "informal" AND location = "justus lipsius building, brussels" AND date = "23 may"