package no065;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int k = sc.nextInt();
		double[][] a = new double[k][k];
		double[] b = new double[k];
		for(int i=0;i<k;i++) {
			a[i][i] = 1;
			b[i] = 1;
			for(int j=1;j<=6;j++) {
				if (i + j < k) {
					a[i][i+j] = - 1 / 6D;
				}
			}
		}
		System.out.println(Matrix.solveEquation(a, b)[0]);
	}

}

class Matrix {
	public static final double EPS = 1E-8;
	public static double[][] add(double[][] a,double[][] b) {
		int n = a.length;
		int m = a[0].length;
		double[][] c = new double[n][m];
		for(int i=0;i<n;i++) {
			for(int j=0;j<m;j++) {
				c[i][j] = a[i][j] + b[i][j];
			}
		}
		return c;
	}
	public static double[][] muliply(double[][] a,double k) {
		int n = a.length;
		int m = a[0].length;
		double[][] c = new double[n][m];
		for(int i=0;i<n;i++) {
			for(int j=0;j<m;j++) {
				c[i][j] = a[i][j] * k;
			}
		}
		return c;
	}
	public static double[][] muliply(double[][] a,double[][] b) {
		int n = a.length;
		int m = b[0].length;
		double[][] c = new double[n][m];
		for(int i=0;i<n;i++) {
			for(int j=0;j<m;j++) {
				for(int k=0;k<n;k++) {
					c[i][j] += a[i][k] * b[k][j];
				}
			}
		}
		return c;
	}
	//disruptive
	public static double[] solveEquation(double[][] A,double[] b) {
		int n = A.length;
		double[][] B = new double[n][n+1];
		for(int i=0;i<n;i++) {
			for(int j=0;j<n;j++) {
				B[i][j] = A[i][j];
			}
			B[i][n] = b[i];
		}
		for(int i=0;i<n;i++) {
			int pivot = i;
			for(int j=i;j<n;j++) {
				if (Math.abs(B[j][i]) > Math.abs(B[pivot][i])) {
					pivot = j;
				}

			}
			swapRow(B, i, pivot);
			if (Math.abs(B[i][i]) < EPS) {
				return null;
			}
			for(int j=i+1;j<=n;j++) {
				B[i][j] /= B[i][i];
			}
			for(int j=0;j<n;j++) {
				if (i==j) {
					continue;
				}
				for(int k=i+1;k<=n;k++) {
					B[j][k] -= B[j][i] * B[i][k];
				}
			}
		}
		double[] x = new double[n];
		for(int i=0;i<n;i++) {
			x[i] = B[i][n];
		}
		return x;
	}
	public static void swapRow(double[][] A,int i,int j) {
		double[] temp = A[i];
		A[i] = A[j];
		A[j] = temp;
	}
}