```python
def path_clean(path: str) -> str:
    """
    Remove every segment of two dots by dropping it together with the segment standing before it,
    and return what remains joined by slashes. Two dots with nothing before them are dropped alone.
    """
    if not path:
        return path

    cleaned_path = []
    for segment in path.split('/'):
        if segment == '..':
            if cleaned_path and cleaned_path[-1] != '..':
                cleaned_path.pop()
        elif segment != '.':
            cleaned_path.append(segment)

    return '/'.join(cleaned_path)
```