import java.math.BigDecimal;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		
		BigDecimal A0 = BigDecimal.valueOf(4.0);
		BigDecimal A1 = BigDecimal.valueOf(4.0);
		
		final BigDecimal nineteen = BigDecimal.valueOf(19);
		final BigDecimal twelve = BigDecimal.valueOf(12);
		final BigDecimal four = BigDecimal.valueOf(4);
		
		for(int i = 0; i < N - 1; i++){			
			final BigDecimal value = A0.multiply(nineteen).subtract(A1.multiply(twelve)).divide(four);
			
			A0 = A1; A1 = value;
		}
		
		if(N == 0){
			System.out.printf("%.12f\n", 4.0);
		}else if(N == 1){
			System.out.printf("%.12f\n", 3.0);
		}else{
			System.out.printf("%.12f\n", A1);
		}
	}

}