import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		
		final int K = sc.nextInt();
		final int size = 6 * K;
		
		double[][] ok = new double[K + 1][size + 1];
		double[] over = new double[K + 1];
		
		ok[0][0] = 1;
		for(int i = 1; i <= 6; i++){
			ok[1][i] = 1.0 / 6;
		}
		
		for(int i = 2; i <= K; i++){
			for(int j = 0; j <= size; j++){
				
				for(int k = 1; k <= 6; k++){
					final int index = j - k;
					if(index < 0){ continue; }
					if(index >= K){ continue; }
					
					ok[i][j] += ok[i - 1][index] / 6;
				}
			}
		}
		
		for(int i = 1; i <= K; i++){
			for(int j = 1; j <= 5; j++){
				final int index = K - j;
				if(index < 0){ continue; }
				if(index >= K){ continue; }
				
				//System.out.println(i + " " + j + " " + index);
				over[i] += ok[i - 1][K - j] * (1.0 - j / 6.0);
			}
		}
		
		//System.out.println(Arrays.toString(ok[1]));
		//System.out.println(Arrays.toString(ok[2]));
		//System.out.println(Arrays.toString(over));
		
		double upper_sum = 0;
		for(int i = 1; i <= K; i++){
			upper_sum += (ok[i][K] + over[i]) * i;
		}
		final double over_sum = Arrays.stream(over).sum();
		
		System.out.printf("%.8f\n", (upper_sum / (1.0 - over_sum)));
	}

}