A company in China signed a CIF export contract with a foreign businessman, using the L / C payment method. The letter of credit issued by a foreign bank stipulated, "The validity period of the letter of credit is August 10, and the latest shipment period is July 31." The Chinese company speeded up the shipment of the goods and obtained the mate's receipt on July 21, and further obtained the original clean onboard bill of lading, we should present the documents to the bank no later than __________.