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## old index value
en_l = 1 
factorial = 1
## to calculate n factorial
n = 1  ## iteration variable
invfactorial = 1  ## inverse of n factorial

# while True:
#     en = en_l + invfactorial
#     n = n + 1
#     factorial = factorial * n
#     invfactorial = 1.0/factorial
#     en_l = en
#     if invfactorial > 1e-6:
#         pass
#     else:
#         break

 while invfactorial > 1e-6:
    en = en_l + invfactorial
    n = n + 1
    factorial = factorial * n
    invfactorial = 1.0/factorial
    en_l = en
     
# print("e = %-.5f"%en)
print("e =", round(en, 5))
# e = 2.71828
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def factorial(num):
    """求阶乘"""
    result = 1
    for n in range(1, num + 1):
        result *= n
    return result