import java.util.Scanner;


public class Main_yukicoder75_1 {

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

        int k = sc.nextInt();

        double[] dp = new double[k + 1];
        double l = 0;
        double r = 1000;
        for (int loop = 0; loop < 40; loop++) {
        	double mid = (l + r) / 2;
        	for (int i = k - 1; i >= 0; i--) {
        		double tmp = 1.0;
        		for (int j = 1; j <= 6; j++) {
        			if (i + j > k) {
        				tmp += mid / 6;
        			} else {
        				tmp += dp[i + j] / 6;
        			}
        		}
        		dp[i] = tmp;
        	}
        	
        	if (dp[0] > mid) {
        		l = mid;
        	} else {
        		r = mid;
        	}
        }

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

        sc.close();
    }
}