package no044;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] dp = new long[n+1];
		dp[0] = 1;
		for(int i=1;i<=n;i++) {
			if (i > 1) {
				dp[i] += dp[i-2];
			}
			dp[i] += dp[i-1];
		}
		System.out.println(dp[n]);
	}

}