#!/usr/bin/python3
from math import gamma

def factorial(n):
	n = int(n)
	result = 1
	if(n < 0):
		raise ValueError("n must be greater than 0")
	if(n == 0):
		return result
	for i in range(1, n + 1):
		result *= i
	return result

if( __name__ == "__main__"):
	print("factorial(5) = ", factorial(5))

	print("gamma(6) = ", gamma(6))