import java.util.*;
import java.io.*;
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		PrintWriter ou = new PrintWriter(System.out);
		int k = Integer.parseInt(sc.next());
		double a = Math.PI * Math.PI / 6;
		if(k != 0){
			a = 0;
			for(int i = 1 ; i <= k ; i++){
				a += 1. / i;
			}
			a /= k;
		}
		ou.println(a);
		sc.close();
		ou.flush();
	}
}