# Solution

def factorial(n):
    """
    Calculate n!

    Args:
       n(int): factorial to be computed
    Returns:
       n!
    """

    if n == 0:
        return 1  # by definition of 0!
    return n * factorial(n-1)

print ("Pass" if (1 == factorial(0)) else "Fail")
print ("Pass" if  (1 == factorial(1)) else "Fail")
print ("Pass" if  (120 == factorial(5)) else "Fail")