#!/usr/bin/env python3
"""
Usage: deepestdir [<ROOT>]

Prints the path to the deepest directory under the given root.  If no root
is given, the current directory is used.  If there are multiple directories
at the same depth, only one is printed.
"""

import functools
import os
import sys


def get_dir_paths_under(root):
    """Generates the paths to every directory under ``root``."""
    for dirpath, dirnames, _ in os.walk(root):
        for d in dirnames:
            yield os.path.join(dirpath, d)


@functools.cache
def directory_depth(d):
    """Returns the depth of a directory in the filesystem."""
    if os.path.dirname(d) == d:
        return 0
    else:
        return 1 + directory_depth(os.path.dirname(d))


if __name__ == "__main__":
    try:
        root = sys.argv[1]
    except IndexError:
        root = "."

    print(max(get_dir_paths_under(root), key=directory_depth))