// 2024 IUSB Programming Competition
// Round 1 Problem 1
// Majic Function
// Solution by Liguo Yu

import java.util.Scanner;

public class round1_p1
{
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        int n = input.nextInt();
        double result = 3;
        
        for (int i=1; i<=n; i++)
        {
            result = result + Math.pow(-1, i+1)*4.0/(2*i*(2*i+1)*(2*i+2));
        }

        System.out.println(result);
    }
}