Question: How many minutes did the current goalkeeper for Borussia Dortmund remain unbeaten at his previous club?
{'answer': '659', 'supporting_facts': [['2012–13 Grasshopper Club Zürich season', 0], ['2012–13 Grasshopper Club Zürich season', 1], ['2012–13 Grasshopper Club Zürich season', 2], ['Roman Bürki', 0], ['Roman Bürki', 1]]}