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]);
        }
    }
}