import java.util.Scanner;

public class Main {

	@SuppressWarnings("resource")
	public static void main(String args[]) {
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		dfs(0,n);
		System.out.println(cnt);
	}

	static long cnt=0;
	private static void dfs(int i,int n) {
		if(i>=n){
			if(i==n)cnt++;
			return;
		}
		dfs(i+1,n);
		dfs(i+2,n);
		
	}
}