@timer
def calc_factorial(num):
    if (num < 0):
        raise ValueError('Please use a number not smaller than 0')
    product = 1
    for i in range(num):
        product = (product * (i + 1))
    return product
@timer
def calc_factorial(num):
    if (num < 0):
        raise ValueError('Please use a number not smaller than 0')
    product = 1
    for i in range(num):
        product = (product * (i + 1))
    return product