import java.math.BigDecimal;
import java.util.Scanner;

public class Main
{
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int N = scanner.nextInt();
		BigDecimal[] A = new BigDecimal[101];
		A[0]= new BigDecimal(4);
		A[1] = new BigDecimal(3);

		for (int i = 2; i <= N; i++) {
			BigDecimal a = A[i - 1].multiply(new BigDecimal(19));
			BigDecimal b = A[i - 2].multiply(new BigDecimal(12));
			A[i] = a.subtract(b).divide(new BigDecimal(4));
		}

		System.out.println(A[N]);
    }

}