import java.util.Scanner;
public class P10870 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println(fibo(sc.nextInt()));
sc.close();
}
private static int fibo(int n) {
if (n <= 1)return n;
return fibo(n - 1) + fibo(n - 2);
}
}