import java.io.*;
import java.util.Scanner;


public class Main_yukicoder786 {

	private static Scanner sc;
	private static Printer pr;

	private static void solve() {
		int n = sc.nextInt();

		long[] dp = new long[n + 1];
		dp[0] = 1;
		
		for (int i = 0; i < n; i++) {
			dp[i + 1] += dp[i];
			if (i + 2 <= n) {
				dp[i + 2] += dp[i];
			}
		}
		
		pr.println(dp[n]);
	}

	// ---------------------------------------------------
	public static void main(String[] args) {
		sc = new Scanner(System.in);
		pr = new Printer(System.out);
			
		solve();
			
		pr.close();
		sc.close();
	}

	static class Printer extends PrintWriter {
		Printer(OutputStream out) {
			super(out);
		}
	}
}