import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
       
        Scanner scan = new Scanner(System.in);
        
        int K = scan.nextInt();
        
        double sum = 0;
        double ans = calc(K , 0 , sum);
        
        System.out.println(String.format("%.10f" , ans));
    }
    
    private static double calc(int K , int num , double sum){
        
        if(num >= K){
            return 0;
        }
        
        sum = sum + calc(K , num+1 , sum) / 6 + calc(K , num+2 , sum) / 6 + calc(K , num+3 , sum) / 6 + calc(K , num+4 , sum) / 6 + calc(K , num+5 , sum) / 6 + calc(K , num+6 , sum) / 6 + 1;
        
        return sum;
        
    }
    
}