context: The evacuation of the second BEF took place during Operation Ariel between 15 and 25 June. The Luftwaffe, with complete domination of the French skies, was determined to prevent more Allied evacuations after the Dunkirk debacle. 1st Air Corps (Germany) was assigned to the Normandy and Brittany sectors.  On 9 and 10 June, the port of Cherbourg was subject to 15 tonnes of German bombs, while Le Havre received 10 Bombing of France during World War II that sank 2,949 Gross register tonnage of escaping Allied shipping. On 17 June, Junkers Ju 88s—mainly from Kampfgeschwader 30—sank a "10,000 tonne ship" which was the 16,243 GRT liner  off St Nazaire, killing some 4,000 Allied personnel (nearly doubling the British killed in the battle of France). Nevertheless, the Luftwaffe failed to prevent the evacuation of some 190,000-200,000 Allied personnel.
question: How many days after the start of the evacuation of the second BEF did the Junkers Ju 88s sink the ship?
answer: 2