



from math import factorial


def      UpperCamelCase(    __UpperCamelCase				:						int = 20					):
		lowerCAmelCase_     :	List[str]							   =					2 * n  # middle entry of odd rows starting at row 3 is the solution for n = 1,
		# 2, 3,...
		lowerCAmelCase_     :	List[Any]							   =					n // 2

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


if __name__ == "__main__":
						import sys

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







'''simple docstring'''
def 		A_(     A						:		list[int]):
							UpperCamelCase   			=     []
							if len(A) == 1:
														return [nums.copy()]
							for _ in range(len(A)):
														UpperCamelCase   			=     nums.pop(0)
														UpperCamelCase   			=     permute(A)
														for perm in permutations:
																					perm.append(A)
														result.extend(A)
														nums.append(A)
							return result







def 		A_(     A						:		str):

							def backtrack(A						:		str):
														if start == len(A) - 1:
																					output.append(nums[:])
														else:
																					for i in range(A		,     len(A)):
																												UpperCamelCase			,	UpperCamelCase   			=     nums[i], nums[start]
																												backtrack(start + 1)
																												UpperCamelCase			,	UpperCamelCase   			=     nums[i], nums[start]  # backtrack

							UpperCamelCase   			=     []
							backtrack(0)
							return output


if __name__ == "__main__":
						import doctest

						# use res to print the data in permute2 function
						lowerCAmelCase					:    Dict           = permutea([1, 2, 3])
						print(res)
						doctest.testmod()




