Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
what's the highest lap that contains the driver of graham hill and a grid that is larger than 18?

### Inputs:
table_name: table, columns: ['Driver', 'Constructor', 'Laps', 'Time/Retired', 'Grid']

### Response:
SELECT MAX Laps FROM table WHERE Driver = graham hill AND Grid > 18