package no053;

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

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		BigDecimal x0 = new BigDecimal("4");
		BigDecimal x1 = new BigDecimal("3");
		BigDecimal c1 = new BigDecimal("19");
		BigDecimal c2 = new BigDecimal("-12");
		BigDecimal c3 = new BigDecimal("4");
		if (n <= 1) {
			if (n == 0) {
				System.out.println(x0);
			}else{
				System.out.println(x1);
			}
			return;
		}
		BigDecimal x2 = BigDecimal.ZERO;
		for(int i=0;i<n-1;i++) {
//			System.out.println(x2);
			x2 = x1.multiply(c1).add(x0.multiply(c2)).divide(c3);
			x0 = x1;
			x1 = x2;
		}
		if (x2.compareTo(new BigDecimal("1E-9")) <= 0) {
			System.out.println(0);
		}else{
			System.out.println(x2.setScale(10,BigDecimal.ROUND_HALF_EVEN).toPlainString());
		}
	}

}