def fact(num):
    if num == 0:
        return 1
    elif num < 0:
        print(f"{num} is Negative please enter positive number ")
    else:
        return num * fact(num - 1)


num = int(input("Enter a positive number calculate its factorial: "))
result = fact(num)
if result is not None:
    print(f"{num}! = {result}")