import java.io.*;
public class Ex030205{
	static double method(int n){
		double xn=1.0;
				
		for (int i=2;i<=n;i++){
			xn=xn+1.0/((i-1)*i);
		}
		return xn;
	}
	public static void main(String[] args){
		int n=0;
		Reader ir = new InputStreamReader(System.in);
		BufferedReader r = new BufferedReader(ir);
		String sc="";
		System.out.print(" n = ");
		try{
			sc = r.readLine();
		}catch (IOException e){}
		try{
			n=Integer.parseInt(sc);
		}catch (NumberFormatException e){
			System.out.println("輸入的數據不是整數");
			System.exit(1);
		}
		System.out.println("xn = "+method(n));
	}
}