import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        System.out.println(getall(n));
    }
    public static int getold(int n){
        if (n<3) {
            return 0;
        }if (n==3) {
            return 1;
        }
        else {
            return getall(n-2);
        }

    }
    public static int getall(int n){
        if (n<=3) {
            return 1;
        }else {
            return getall(n-1)+getold(n-1);
        }
    }
}