include

using namespace std;

int main() {

int a = 2, b = 1;
int n;
cin >> n;
double sum = 0;
for (int i = 1; i <= n; i++) {
	sum += 1.0 * a / b;
	int t = a;
	a = a + b;
	b = t;
}
printf("%.2lf", sum);
return 0;

}