#include <stdio.h>
int main(void) {
	int n, s,i,j;
	s = 0;
	int m;
	scanf("%d", &n);
	for (i = n; i >= 1; i--) {
		m = 1;
		for (j = i; j >= 1; j--) {
			m = m * j;
		}
		s = s + m ;
	}
	printf("%d", s);
	return 0;
}