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[1000][];
		for(int i=0;i<1000;i++) ans[i] = new double[1000];
		
		Parallel.For(0,1000,i=>{
			Parallel.For(0,1000,j=>{
				for(int k=1;k<1000;k++){
					double s=(X+1000000.0*i+1000*j+k);
					ans[i][j] += 1/s/s;
				}
			});
		});
		
		double ret = 0;
		for(int i=0;i<1000;i++){
			for(int j=0;j<1000;j++){
				ret += ans[i][j];
				if( i!=0 || j != 0)ret += 1/(X+1000000.0*i+1000*j)/(X+1000000.0*i+1000*j);
			}
		}
		Console.WriteLine(ret);
		
		
	}
	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));}
}