import java.util.Scanner;

/**
 * 【统计每个月兔子的总数】
 *
 */
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int nextInt = sc.nextInt();

        System.out.println(getCount(nextInt));

    }

    public static int getCount(int nextInt) {
        if (nextInt == 1 || nextInt == 2) {
            return 1;
        }
        return getCount(nextInt - 1) + getCount(nextInt - 2);
    }
}