user: Question: what is the least laps when the driver is rolf stommelen and the grid is more than 18?
Columns: ['Driver', 'Constructor', 'Laps', 'Time/Retired', 'Grid']
Types: ['text', 'text', 'real', 'text', 'real']
Sample row: ['Jacky Ickx', 'Ferrari', 70.0, '1:56:20.0', 1.0]
SQL:

assistant: SELECT MIN("Laps") FROM "Table" WHERE "Driver" = 'rolf stommelen' AND "Grid" > 18.0;