import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int K = sc.nextInt();
        double [] E = new double [K+5];
        E[K]=E[K+1]=E[K+2]=E[K+3]=E[K+4]=0;
        E[K-1]=1;
        for(int i=K-2; i>=0; i--){
            E[i]=1+(E[i+1]+E[i+2]+E[i+3]+E[i+4]+E[i+5]+E[i+6])/6.0;
        }
        System.out.println(E[0]);
    }
}