import java.util.Scanner;

public class Main65 {
	public static void main(String[] args) {
		Main65 p = new Main65();
	}

	public Main65() {
		Scanner sc = new Scanner(System.in);
		
		int k = sc.nextInt();
		
		solve(k);
	}

	public void solve(int k) {
		double[] dp = new double[k+1];
		
		for(int i=1;i<dp.length;i++){
			for(int j=1;j<=6;j++){
				if(i-j<1)
					break;
				dp[i] += dp[i-j] / 6.0;
			}
			dp[i] += 1;
		}
		
		System.out.println(dp[k]);
		
	}

}