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

### Instruction:
Which constructor had a Time/Retired of collision, where the grid number was less than 18 and Nick Heidfeld was the driver?

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

### Response:
SELECT Constructor FROM table WHERE Time/Retired = collision AND Grid < 18 AND Driver = nick heidfeld