import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int k = sc.nextInt();
		sc.close();

		double ans = 0;
		for (int i = 1; i < 3000000; i++) {
			ans += 1.0 / i / (i + k);
		}
		System.out.println(ans);
	}
}