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

### Instruction:
How many years did BBC One rank 20th?

### Inputs:
table_name: table, columns: ['Year', 'Broadcast date', 'BBC One total viewing', 'BBC One Rank', 'BBC Two total viewing', 'BBC Two Rank']

### Response:
SELECT COUNT Year FROM table WHERE BBC One Rank = 20th