include

using namespace std;

int main() {

long long k;
long long rt = 0;
cin >> k;
long long n, sum;

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

	sum = 1;

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

		sum *= j;
	}

	rt += sum;
}

cout << rt;
return 0;

}