include

using namespace std;

int main() {

int a,b=1,c,d=0;
cin >> c;
for (int i = 1; i <= c; i++) {
	b = 1;
	for (int j = 1; j <= i; j++) {
		b = b * j;
	}
	d = d + b;
}
cout << d;
return 0;

}