include

using namespace std;

int main () {

int n = 0, g = 1, a, k, b = 0;
cin >> k;

for (int a = 1; a <= k; a++) {

	g = 1;

	for (int i = 1; i <= a; i++) {

		g = g * i;
	}

	b = g + b;
}

cout << b;

return 0;

}