CREATE TABLE table_54598 ("Year" FLOAT, "Date" TEXT, "Type" TEXT, "President" TEXT, "Location" TEXT)

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?
SELECT SUM("Year") FROM table_54598 WHERE "Type" = 'informal' AND "Location" = 'justus lipsius building, brussels' AND "Date" = '23 may'
SELECT SUM("Year") FROM "table_54598" WHERE "Date" = '23 may' AND "Location" = 'justus lipsius building, brussels' AND "Type" = 'informal'