import java.util.Scanner;

/**
 * Created by whiled on 17/05/04.
 */
public class Main {
    public static void main(String[] args) {
        int N = (new Scanner(System.in)).nextInt();

        long[] res = new long[N+1];
        res[0] = 1;
        res[1] = 1;

        for (int i=2; i<=N; i++){
            res[i] = res[i-2] + res[i-1];
        }

        System.out.println(res[N]);
    }
}