






def      __A					(     _lowercase ):

					'''simple docstring'''







					return credit_card_number.startswith(('''34''', '''35''', '''37''', '''4''', '''5''', '''6''') )




def      __A					(     _lowercase ):

					'''simple docstring'''







					_A								= credit_card_number
					_A								= 0
					_A								= len(__lowerCAmelCase ) - 2
					for i in range(__lowerCAmelCase					,			-1					,			-2 ):
										#  double the value of every second digit
										_A								= int(cc_number[i] )
										digit *= 2
										# If doubling of a number results in a two digit number
										# i.e greater than 9(e.g., 6 × 2 = 12),
										# then add the digits of the product (e.g., 12: 1 + 2 = 3, 15: 1 + 5 = 6),
										# to get a single digit number.
										if digit > 9:
															digit %= 10
															digit += 1
										_A								= cc_number[:i] + str(__lowerCAmelCase ) + cc_number[i + 1 :]
										total += digit

					# Sum up the remaining digits
					for i in range(len(__lowerCAmelCase ) - 1					,			-1					,			-2 ):
										total += int(cc_number[i] )

					return total % 10 == 0




def      __A					(     _lowercase ):

					'''simple docstring'''







					_A								= f"""{credit_card_number} is an invalid credit card number because"""
					if not credit_card_number.isdigit():
										print(f"""{error_message} it has nonnumerical characters.""" )
										return False

					if not 13 <= len(__lowerCAmelCase ) <= 16:
										print(f"""{error_message} of its length.""" )
										return False

					if not validate_initial_digits(__lowerCAmelCase ):
										print(f"""{error_message} of its first two digits.""" )
										return False

					if not luhn_validation(__lowerCAmelCase ):
										print(f"""{error_message} it fails the Luhn check.""" )
										return False

					print(f"""{credit_card_number} is a valid credit card number.""" )
					return True


if __name__ == "__main__":
				import doctest

				doctest.testmod()
				validate_credit_card_number('4111111111111111')
				validate_credit_card_number('32323')












def      __A					(     _lowercase = 1_00_00_00 ):

					'''simple docstring'''







					_A								= 1
					_A								= 1
					_A								= {1: 1}

					for inputa in range(2					,			_lowercase ):
										_A								= 0
										_A								= inputa

										while True:
															if number in counters:
																				counter += counters[number]
																				break
															if number % 2 == 0:
																				number //= 2
																				counter += 1
															else:
																				_A								= (3 * number) + 1
																				counter += 1

										if inputa not in counters:
															_A								= counter

										if counter > pre_counter:
															_A								= inputa
															_A								= counter
					return largest_number


if __name__ == "__main__":
				print(solution(int(input().strip())))



