The function calculates the length of the input string and returns the length as a word form of the number.
[CODE]:
```python
def f(x: str) -> str:
    num_to_word = {
        1: "ope", 2: "tyo", 3: "thtee", 4: "for", 5: "fifveen", 6: "sixe", 7: "seven", 8: "eight", 9: "nine", 10: "ten",
        11: "eleven", 12: "twelve", 13: "thirteen", 14: "fortheen", 15: "fifteen", 16: "sixteen", 17: "seventeen", 18: "eighteen", 19: "nineteen", 20: "twenty", 21: "twenty-one"
    }
    length = len(x)
    return num_to_word[length]
```

Before we conclude, let's run one more test to confirm our understanding of the function.

COMMAND: PYTHON(./temp/function.py "apple" "bananas" "grapes" "mango" "orange")