import java.util.Scanner;


public class Main_yukicoder65 {

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

        int k = sc.nextInt();

        double[] e = new double[k + 1];
        e[k] = 0.0;
        for (int i = k - 1; i >= 0; i--) {
        	e[i] = 1;
        	for (int j = 0; j < 6; j++) {
        		if (i + j + 1 <= k) {
        			e[i] += e[i + j + 1] / 6;
        		}
        	}
        }

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

        sc.close();
    }
}