import java.util.Scanner;
public class Main {
    
    // 计算小乐乐可以走的方法数
    public static int show(int n) {
        if(n == 1) {
            return 1;
        } else if(n == 2) {
            return 2;
        } else {
            return show(n-1)+show(n-2);
        }
    }
    
    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int result = show(n);
        System.out.println(show(n));
    }
}