#include <stdio.h>
long long jc(long long x);

int main (void) {
	long long n;
	unsigned long long s=0;
	scanf("%lld", &n);
	for (int i = 1; i < n + 1; i++)
		s += jc(i);
	printf("%llu", s);

	return 0;
}

long long jc(long long x) {
	long long a = 1;
	for (long long j = 1; j <= x; j++)
		a *= j;

	return a;
}