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

class Sol{
	public void Solve(){
		
		double[] ans = new double[100000];
		Parallel.For(0,100000,i=>{
		//for(int i=0;i<100000;i++){
			for(int j=1;j<10000;j++){
				ans[i] += 1.0/(X+i*10000+j)/(X+i*10000+j);
			}
			//Console.WriteLine(ans[i]);
		//}
		});
		
		for(int i=1;i<100000;i++) ans[i] += 1.0/(X+i*10000)/(X+i*10000);
		
		Console.WriteLine("{0:F12}",ans.Sum());
		
	}
	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));}
}