import java.math.BigInteger;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        BigInteger mul = new BigInteger(String.valueOf(2));

        BigInteger[] arr = new BigInteger[1003];

        arr[1] = new BigInteger(String.valueOf(2));

        arr[2] = new BigInteger(String.valueOf(5));

        arr[3] = new BigInteger(String.valueOf(13));

        for (int i = 4; i <= 1000; i++) {

            arr[i] = ((arr[i - 1].multiply(mul)).add(arr[i - 2]));

            arr[i] = arr[i].add(arr[i - 3]);
        }

        Scanner sc = new Scanner(System.in);
        
        int num;

        while (sc.hasNext()) {
            
            num = sc.nextInt();
            
            System.out.println(""+arr[num]);
        }
    }
}