#factorial: int -> int
#cfactorial de entero n >= 0
#ej: factorial(4) -> 24
#ej: factorial(0) -> 1
 
def factorial(n):
    assert type(n)==int and n>=0
    if n == 0 :
        return 1
    else:
        return factorial(n-1)  * n

assert factorial(4)==24
assert factorial(0)==1

def factorial(n):
    assert type(n)==int and n>=0
    if n<=1 : return 1
    return n * factorial(n-1)