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

class Sol{
	public void Solve(){
		
		int a=ri();
		
		if(a==0){
			Console.WriteLine(4);
			return;
		}
		if(a==1){
			Console.WriteLine(3);
			return;
		}
		
		a-=1;
		double x=4.0;
		double y=3.0;
		double z=0;
		while(a>0){
			z=(19*y-12*x)/4.0;
			x=y;y=z;a--;
		}
		Console.WriteLine(z);
		
		
	}

	public Sol(){
		
	}




	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(){return Console.ReadLine().Split(' ');}
	static int[] ria(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>int.Parse(e));}
	static long[] rla(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>long.Parse(e));}
	static double[] rda(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>double.Parse(e));}
}