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);
}
}