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

### Instruction:
What Transfer window that has a Transfer fee of free, with a Moving to of derby county?

### Inputs:
table_name: table, columns: ['Nat.', 'Name', 'Moving to', 'Type', 'Transfer window', 'Transfer fee']

### Response:
SELECT Transfer window FROM table WHERE Transfer fee = free AND Moving to = derby county