import java.util.Arrays;
import java.util.Scanner;

public class Main {
	static Scanner in = new Scanner(System.in);
	public static void main(String[] args){
		int N = in.nextInt();
		long t[] = new long[N + 2];
		
		Arrays.fill(t, 0);
		t[0] = 1;
		
		for(int i = 0; i < N; i++){
			t[i + 1] += t[i];
			t[i + 2] += t[i];
		}
		System.out.println(t[N]);
	}
}