user: Question: What is the total number of drivers who have cars constructed by Mercedes-Benz?
Columns: ['Year', 'Formula', 'Driver', 'Constructor', 'Location', 'Report']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1902.0, 'Grand Prix', 'Charles Jarrott', 'Panhard 70', 'Bastogne', 'Report']
SQL:

assistant: SELECT COUNT("Driver") FROM "Table" WHERE "Constructor" = 'Mercedes-Benz';