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_15088557_1 (stage INTEGER, mountains_classification VARCHAR, winner VARCHAR)
### Question:
what is the minimum stage where mountains classification is aitor osa and aitor gonzález won?
### Answer:
SELECT MIN(stage) FROM table_15088557_1 WHERE mountains_classification = "Aitor Osa" AND winner = "Aitor González"