using System;
using System.Collections;
using System.Collections.Generic;
 
class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	public void Solve(){
		
		double[][] P=new double[2][];
		P[0]=new double[K+1];
		P[1]=new double[K+1];
		int cnt=0;
		double eps=1e-9;
		
		double E=0.0;
		double Eprev=0.0;
		P[0][0]=1.0;
		while(true){
			cnt++;
			int next=cnt%2;
			int now=1-next;
			E=Eprev;
			P[next]=new double[K+1];
			for(int i=0;i<K;i++){
				for(int d=1;d<=6;d++){
					if(i+d<=K)P[next][i+d]+=P[now][i]*1.0/6.0;
					else P[next][0]+=P[now][i]*1.0/6.0;
				}
			}
			E+=cnt*P[next][K];
			if(cnt>200 && Math.Abs(E-Eprev)<eps)break;
			Eprev=E;
		}
		
		Console.WriteLine(E);
	}
	int K;
	public Sol(){
		K=ri();
	}




	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(){return Console.ReadLine().Split(' ');}
	static int[] ria(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>int.Parse(e));}
	static long[] rla(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>long.Parse(e));}
	static double[] rda(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>double.Parse(e));}
}