What is the oldest year with a main span feet of 1,640 in South Korea?
CREATE TABLE table_name_52 (
    year_opened INTEGER,
    main_span_feet VARCHAR,
    country VARCHAR
)
SELECT MIN(year_opened) FROM table_name_52 WHERE main_span_feet = "1,640" AND country = "south korea"
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 oldest year with a main span feet of 1,640 in South Korea? ### Input: CREATE TABLE table_name_52 (
    year_opened INTEGER,
    main_span_feet VARCHAR,
    country VARCHAR
) ### Response: SELECT MIN(year_opened) FROM table_name_52 WHERE main_span_feet = "1,640" AND country = "south korea"