Classify each of the following as either a letter or a number
1, a, o, 3, 9, 193, d, 23, f, d, p, 500
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.
### Instruction: Classify each of the following as either a letter or a number
### Input: 
### Response: 1, a, o, 3, 9, 193, d, 23, f, d, p, 500