```python
def root_digit(value: int) -> int:
    """
    Fold a whole count down to a single figure by adding its figures together,
    then adding the figures of that answer, again and again until one figure is left.
    A count already standing as one figure is given back as it is.
    
    :param value: The number to fold.
    :return: The single figure result.
    """
    while value >= 10:
        total = 0
        while value > 0:
            total += value % 10
            value = value // 10
        value = total
    return value
```