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

class Main
{
	public static void main (String[] args) throws java.lang.Exception{
		Scanner in = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);
		int n;
		n=in.nextInt();
		double S = 0;
		for (int i = 1; i <= n; i++){
			S += 1.0/(i*(i + 1)); 
		}
		System.out.println(S);
	}
}