using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

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

class Sol{
	public void Solve(){
		
		int n = 0;
		while(X > 1 + 1e-9){
			X--;
			n++;
		}
		
		var tot = f(X);
		for(int i=1;i<=n;i++){
			tot -= 1.0/(X+i)/(X+i);
		}
		
		Console.WriteLine(tot);
		
	}
	
	double f(double x){
		
		if(x < 1e-9) return Math.PI*Math.PI/6.0;
		return 4.0 * (f((x+1)/2.0) + f(x/2.0)) + 1.0/(x+1)/(x+1);
		
	}
	
	
	double X;
	public Sol(){
		X = rd();
	}

	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(char sep=' '){return Console.ReadLine().Split(sep);}
	static int[] ria(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>int.Parse(e));}
	static long[] rla(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>long.Parse(e));}
	static double[] rda(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>double.Parse(e));}
}