import java.util.*;
import java.lang.*;
import java.io.*;

class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner  in = new Scanner(System.in);
		int n, a=1, as=a, b=1;
		double sum=0.0, u=2.0;
		n = in.nextInt();
		for(int i=1, k=2; i<=n; i++, k++)
      	{
      		a=3*b+2*a;
      		b=2*as+b;
      		u*=(2.0/k);
      		sum+=u*(1.0/(1+a*a+b*b));
      		as=a;
      	}
       System.out.printf(Locale.US, "%.8f", sum); 
	}
}