import java.util.Scanner;

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