import java.io.*;
import java.util.*;
import java.math.*;

class Main {
	
	static int k;
	static double[] memo;
	
	public static void out (Object o) {
		System.out.println(o);
	}
	
	public static double E (int x) {
		if (memo[x] != -1) return memo[x];
		if (x >= k) return memo[x] = 0;
		return memo[x] = (E(x + 1) + E(x + 2) + E(x + 3) + E(x + 4) + E(x + 5) + E(x + 6)) / 6.0 + 1;
	}
	
	public static void main (String[] args) throws IOException {
		BufferedReader br = 
			new BufferedReader(new InputStreamReader(System.in));
		
		k = Integer.parseInt(br.readLine());
		memo = new double[k + 6];
		Arrays.fill(memo , -1);
		
		E(0);
		
		out(memo[0]);
	}
}