import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		if (n < 6) {
		    System.out.println(0);
		    return;
		}
		double[][] rates = new double[n][6];
		rates[0][0] = 1;
		for (int i = 1; i < n; i++) {
		    for (int j = 0; j < 6; j++) {
		        if (j == 0) {
		            rates[i][j] = rates[i - 1][j] / 6;
		        } else {
		            rates[i][j] = rates[i - 1][j] * (j + 1) / 6 + rates[i - 1][j - 1] * (6 - j) / 6;
		        }
		    }
		}
		System.out.println(rates[n - 1][5]);
	}
}