Bài 5

import java.util.Scanner;

public class P1 {

	public static float Sol(int n) {
		float s = 0;

		for (int i = 0; i <= n; i++)
			s += 1.0 / (2 * i + 1);

		return s;
	}

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();

		System.out.println(Sol(n));
	}
}