import java.util.Scanner;


public class Main_yukicoder75 {

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

        int k = sc.nextInt();

        double[] e = new double[k + 1];
        final double EPS = 1.e-6;
        double prev = 0;
        while (prev == 0 || e[0] == 0 || Math.abs(prev - e[0]) > EPS) {
        	prev = e[0];
        	for (int i = k - 1; i >= 0; i--) {
        		double tmp = 1.0;
        		for (int j = 1; j <= 6; j++) {
        			if (i + j > k) {
        				tmp += e[0] / 6;
        			} else {
        				tmp += e[i + j] / 6;
        			}
        		}
        		e[i] = tmp;
        	}
        }

        System.out.printf("%.3f\n", e[0]);

        sc.close();
    }
}