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

### Instruction:
What episode aired on 18 April 2007?

### Inputs:
table_name: table, columns: ['#', 'Air Date', 'Challenge', 'Winner', 'Test-taker', 'Passed?']

### Response:
SELECT MIN # FROM table WHERE Air Date = 18 April 2007