import java.math.*;
import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        if(n==0) {
        	System.out.println(4);
        	return;
        }
        double[] aa = new double[n+1];
        aa[0]=4;
        aa[1]=3;
        for(int i=2;i<=n;i++){
        	double a = aa[i-1]*19.0/4;
        	double b = aa[i-2]*3;
        	aa[i]=a-b;
        }
        System.out.println(aa[n]);
    }
}