import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		double k = sc.nextInt();
		double ans = 0;
		for (int i = 1; i < 10000000; i++) {
		    ans += 1 / (i * (i + k));
		}
		System.out.println(ans);
	}
}