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);
		double n;
		n=in.nextDouble();
		double d;
		System.out.printf("%.5f",(50*(1-(Math.pow(0.25,n))))/(0.75));
	}
}