#include <iostream>
using namespace std;
long long factorial(int n);
int main() {
	int n = 0;
	cin >> n;
        //定义为long long
	long long sum = 0;
	for(int i = 1; i <= n; i++)
                //对每个i调用factorial函数求其阶乘
		sum += factorial(i);
	cout << sum ;
	return 0;
}
long long factorial(int i) {
        //这里的result一定要初始化为1
	long long result = 1;
	for(int j = 1; j <= i; j++)
		result*= j;
	return result;
}