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_20 (population INTEGER, colour VARCHAR, construction_commenced VARCHAR)
### Question:
What is the lowest population for the neighborhood with the color blue that commenced its construction before 1987?
### Answer:
SELECT MIN(population) FROM table_name_20 WHERE colour = "blue" AND construction_commenced < 1987