'''

Project Euler: Problem 20: Factorial digit sum

n! means n × (n − 1) × ... × 3 × 2 × 1

For example, 10! = 10 × 9 × ... × 3 × 2 × 1 = 3628800,

and the sum of the digits in the number 10! is

3 + 6 + 2 + 8 + 8 + 0 + 0 = 27.

Find the sum of the digits in the number 100!

Answer: 648

'''

n = 100

fac = 1  #初始化阶乘结果

while n >= 1:

    fac *= n

    n -= 1

# 提取出阶乘结果的每个数字，形成列表lst

lst = [int(i) for i in str(fac)]

res = 0  #初始化相加结果

for i in range(len(lst)):

    res += lst[i]

print(res)