说明

Given a positive integer, n , which is lower than 21, please write a program to calculate the sum of factorials of 1, 2, ... n.


The formula is defined as:

S(n)=1!+2!+3!+4!+5!+…+n!


For example:  3!=1*2*3

输入格式

n，one positive integer which is lower than 21

输出格式

One positive integer, S(n), which is defined as the formula shown above.

5

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