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_4 (frequency INTEGER, callsign VARCHAR)
### Question:
What's the highest frequency of the KBDR callsign?
### Answer:
SELECT MAX(frequency) FROM table_name_4 WHERE callsign = "kbdr"