





from math import factorial


def     SCREAMING_SNAKE_CASE			(      lowerCAmelCase = 20					):
       _UpperCamelCase              =						2 * n  # middle entry of odd rows starting at row 3 is the solution for n = 1,
       # 2, 3,...
       _UpperCamelCase              =						n // 2

       return int(factorial(lowerCAmelCase					) / (factorial(lowerCAmelCase					) * factorial(n - k					))					)


if __name__ == "__main__":
       import sys

       if len(sys.argv) == 1:
              print(solution(20))
       else:
              try:
                     lowercase    : Dict    	=  int(sys.argv[1])
                     print(solution(n))
              except ValueError:
                     print("""Invalid entry - please enter a number.""")













from __future__ import annotations

from collections.abc import Iterator

class  __A:

     def __init__(      self,       A      ):





            """simple docstring"""

            _UpperCamelCase              =						value
            _UpperCamelCase              =						None
            _UpperCamelCase              =						None






class  __A:

     def __init__(      self,       A      ):





            """simple docstring"""

            _UpperCamelCase              =						tree

     def 	_UpperCamelCase     (      self,       A      ):





            """simple docstring"""

            if node is None:
                   return 0
            return node.value + (
                self.depth_first_search(node.left      ) + self.depth_first_search(node.right      )
            )



     def __iter__(      self      ):





            """simple docstring"""

            yield self.depth_first_search(self.tree      )


if __name__ == "__main__":
       import doctest

       doctest.testmod()






