The function f(x) counts the occurrences of the letter "a" in the input string x and returns the count as a spelled-out number.

[CODE]:
```python
def count_a(input_string):
    count = input_string.count("a")
    number_words = {0: "zero", 1: "one", 2: "two", 3: "three", 4: "four", 5: "five", 6: "six", 7: "seven", 8: "eight", 9: "nine"}
    return number_words[count]

result = count_a("sample")  # result would be "two"
```